(This happens if you run incompatible mods) The Twilight Forest mod itself is a major mod. finally, there has been a on going bug that allows mobs to spawn at the edge of the current loaded chunks, putting some of them into the unloaded chunks. Better catch em in bastion if you want a bartering system, farming piglins is hard, giving how often they do spawn in your gold farm. It's a loooooong-standing bug with the minecraft spawn engine calculation not accounting for render distances lower than the radius in which the engine allows mobs to spawn. Light up every spawnable surface everywhere, out to a minimum distance of 128 blocks from the spawner in all directions. 1)No. You might be having a mob cap problem. Many players complain about mobs not spawning in their farms. But the spawner is definitely the one doing this. I'm going to guess that starting a LAN must have broken the modpack. Oct 21st 2020. Otherwise they would take up precious space in the mob cap. Adding a second row of. Any old farm tutorials might eb outdated. Built a dark room 25 or so blocks high in the sky the roof of it can't spawn anything because of half slabs but there aren't any mobs spawning inside of it. Mob spawning. There's a solution to this. It doesn't work very well, no new pigmen spawn in when the first few are killed. Everything ou are doing is fine. You have to be near it or at least in the general vicinity . They probsbly are spawning but arent dropping down hard to tell. The reason is because mobs only spawn from 148 blocks away from caves, if it is closer, the mobs will spawn in the caves instead of the mob farm. That should work unless the server has some weird plugin that changes the. So if its day the light level will be 15-12 on the bottomside of the block hence disabling spawning. Also, make sure you stand within 32 blocks away from the spawner so they keep spawning. Evokers will rarely spawn as a raid captain, having a. I saw them spawn on the grass dirt. Mobs cannot spawn within 24 blocks of a player. GameStop Moderna Pfizer Johnson & Johnson AstraZeneca Walgreens Best Buy Novavax SpaceX Tesla. It's about 5 chunks away from land to avoid hostile mobs spawning in nearby caves preventing the slime from spawning. For myself, this happens with every spawner trap I make. This forces mobs to only spawn in your farm. If you want just creepers, you need to remove the buttons and put trapdoors on the ceiling of each layer. 2. Make sure both these points are met, or else your mobs will not spawn. The caves under the farm are lighted. Not completely sure: In the end enderman can only spawn on end stone but can teleport to other blocks. I'm often AFK over 24 blocks away from my farm but still no spawns. You will get zombie pigmen to spawn in your trap eventually, but. Since the space under the slabs/trapdoor is a 1 block space, nothing will be able to spawn there and baby zombies shouldn't be able to escape. Here is my farm about 97% completed. 4. ago. They’re rare in soul valley. Business, Economics, and Finance. yess. That means you need to be a specific distance from the spawn area for it to work at all. I built one but I aways had to go to certain Y and afk there to make my xp farm spawn the mobs. Mob traps built close to the sky limit have been known to end up not being completely loaded by the engine in some situations. You've stumbled upon a Bedrock Edition spawning mechanic, "mob density caps". The spawning area is not dark enough (make a roof and do not use torches on the inside). ago. Render distance affects the number of chunks loaded at once. 5. ) but when you work a system from a mob spawner farm that takes the mobs out of the area, then the spawner will instantly spawn another set so it will be a high rate spawner. My case however, is i get way less xp, and it comes out as like 1-10 orbs. and it’s still spawning spiders. Prevent the mobs in the farm from moving. Natural spawn grinders are terribly inefficient if you have a lot of spawnable spaces around. 4 java server, and a zombie spawner farm, and when i saw the video on how to make the farm, when he/she uses it, they get SWARMED by xp. There could be several reasons why your mob farm is not spawning any mobs. This way it will work but it will be slow because the mobs have to move to the water channelsIf you are not visiting this spawner in a long time, glow squids will spawn instead, potentially filling it up with glow ink sacs instead. but yesterday almost nothing came down. 4 java server, and a zombie spawner farm, and when i saw the video on how to make the farm, when he/she uses it, they get SWARMED by xp. For a successful mob farm: Valid spawning spaces (solid blocks). But it feels like they change much more then that. According to wiki: Witches can spawn anywhere in the Overworld at a light level of 7 or less, sometimes in groups of up to three. I've built a mob spawning trap but mobs are not spawning. +, enemy mobs will now only spawn in ''light level 0'' maybe this is the issue, IDK. Tall mobs need a 1x2x1 area to spawn and so the optimal spawning space for them could be 8x5x8. Really appreciate any help, this is my first gold farm in survival. Even when I afk for like half an hour only ten spawn. Build a tower of scaffolding about 110-115 blocks above the farm and build a platform. glass and leaves are both non spawnable blocks. This open block can be filled with signs. 1. Best look up what areas windegos spawn and camp there. I've actually made a zombified piglin farm in my solo world and they are spawning so infrequently as well, I think that it might be because of other mobs below the bedrock ceiling. They spawn when it's dark and there is a solid block above them. However, a player in regular chunks loads in many more mobs than a player that intentionally only loads few spawning platforms in a specialised farm. Commercial-Finish204 • 20 days ago. So it seems like I'm having the same issue as you, as of in the new Minecraft update 1. This is the first in a new tutorial series called Mastering Minecraft where we explore questions about Minecraft. Share. Create Mob Spawning Platforms. 18 Version. I checked it out and it turns out that mobs are spawning but they are kinda just standing still and not moving anywhere, hence they don't move into water. Spawner room is completely dark and I'm being within those 16 blocks :/. Sometimes that will prevent spawning, as the game will just spawn drowned underneath. May 12, 2021. My guess is that the youtube video that you saw was just quite old, therefore it doesn't work anymore in newest minecraft. 0 mod 1. Check to see whether it's complete darkness inside the mob spawner or not. The problem is that mobs only despawn after you are a certain amount of blocks away AND if they are in a high enough light level. • 2 yr. Watch the Spawner Activate. You also need to make sure that when you use your. Mob farms in bedrock edition are pretty bad. I can't adjust the render distance on Realms (no access to server preferences), and my client render is set to 16, so it's not that. When I found it, I immediately torched up the room/spawner to prevent spawns (when I first discovered it on my main account it would spawn like you would expect). This is the minimal height required to instantly kill a Mob. You must be between 16 and 32 blocks away. The reason is because mobs only spawn from 148 blocks away from caves, if it is closer, the mobs will spawn in the caves instead of the mob farm. 1) Fish. Water. You're too close to the farm, as mobs don't spawn closer than 24 blocks of you. Its just good for a better general mob farm and doesnt change xp that much. Keep torches on the wall inside whilst u do it so u don’t get mob spawns whilst it’s half finished. In a fish farm, players can reel in much more than just fish, such as. Mobs won’t spawn in unloaded chunks. See friend, after the 1. Second thing is the farm you showed as a reference will be bad for mob spawning algorithm cuz it's too high up in the sky. . Assuming the player is inside the house with the door closed, only spiders will try to get him. I’m on hard difficulty. Cave spider spawner not spawning anything. Also, at least the spawn platforms must be more than 24 blocks away; mobs don't spawn any closer to the player - so when you come to peek into your farm, all spawns freeze. Okay so I've been playing a little bit of SMP, and I'm now at the point in the game where I need to start creating farms to automate getting tedious materials. . Possible reasons: Farm efficiency greatly decreases the higher it is in the world. The most common trident killers are just. to find some spawners, harvest them and build a mob farm, you can. So recently, i made an enderman farm in my 1. ago. The most obvious is creature spawning. The room is 7 blocks tall. Hopefully, at least one or two mobs will. Mobs start spawning until the mobcap is filled. Hope it was at least somewhat impressive! This is why many darkroom spawner designs have a designated area for the player to stand in so that they are far enough away for mobs to spawn but close enough to keep them moving. 1x3 space needed for spawning, so you should be able to just swap out the current full block ceiling with top slabs. The roof is made of half slabs, but it is still 2 blocks in between the roof and the floor (made of full wood planks). Best look up what areas windegos spawn and camp there. Furthermore, mobs despawn over time when they're more than 30 blocks away, but that. This perticular biome (soul sand valley)doesn't spawn zombified piglins but. The default hostile mob cap is 70 per online player, however after building an enderman farm for XP, I've noticed that only around 30 enderman spawn before the. Making a zombie XP farm in Minecraft. Why won’t creepers spawn in my creeper farm? It does matter that the there are caves or any other areas (that mobs can spawn) vertically in the area of your farm. •. If you want a good xp farm on bedrock I recommend building this. Then you stand in between the spawner and the killing chamber. I looked into it, and found out that there's a very old bug where if the server render distance is set below 10, mobs will barely spawn. The Farm Featured in the Video by Gnembon: • Simple Hostile. r/technicalminecraft • I built one of the most overkill frog light farm in my survival world. Why my XP farm is not working? Try going to Peaceful and back to flush out all the hostiles. Guess it was too easy to farm xp from easy mobs. The truth is that there are a number of bugs that are effecting bedrock edition in respects to mob spawning. I tried the farms on a normal vanilla server and in singelplayer mode and none of them worked. QUEWEX • 4 yr. Is it a river biome? Mobs don't spawn in river biomes. 16 but the youtuber said it would work in 1. Due to being the only natural spawning mob, players can create highly efficient mob farms in the end realm. Mobs instantly despawn when they're more than 128 blocks away, so #1 - you need to be 128 blocks away from any dark spots where you DON'T want mobs to spawn, and #2 - closer than 128 blocks from the farm where you DO want mobs to spawn. Covered here: Can't stop spiders spawning in creeper farm. I've noticed, when updating my 1. The mob limit is exhausted pretty much instantly and the game doesn't spawn any more, unless some of the existing mobs de-spawn or get killed. I stood at the base of the tower for half an hour on hard and I got. I am in "hard" mode and I have built at the height limit (or one block below). Evokers, like other Illagers, will appear in raids but will also appear in Woodland Mansions and drop a very valuable prize when you manage to take them down. I removed bouncy creepers because I tried but couldn't turn off the sound they make. There are a few things that are preventing spawning: The light level is over 7. It's a tower that is 10 blocks long x 5 blocks deep x 35 blocks high. Hardcore guardian XP farm. The mob limit is exhausted pretty much instantly and the game doesn't spawn any more, unless some of the existing mobs de-spawn or get killed. Step 3: Add water and dig the “Hole of Doom”. To put that in perspective, it spawned about 5 mobs in one hour. The most common cause of failure, for mob farms of this type, are due to people forgetting to spawn-proof the area so mobs only spawn in the farm or they build them in SMP and when other players are online they either stop working altogether or slow to. i did build a cow farm next to the mob farm yesterday so i thought that was the problem (cause many entities) so after destroying the cow farm and making it a couple blocks away. [deleted] • 2 yr. The stone slabs are placed as seen, and in the layer below you can see a test I did with carpets being placed in a 3x3 square pattern, covering each corner, and neither technique has worked. Also, try to be withing 32 blocks of the mob farm, because mobs will be guranteed to spawn. 3. A Zombie Pigman farm attached to a mob grinder. If the top of the half-slab is placed at the same height as the top of a full-sized block, then mobs can spawn on it. But now it no longer spawns mobs. A recent update make it so mobs require a light level of 0. But I made a regular farm underground and placed a cube of biome blocks, just like you did and didnt really get any mobs. Attachments. Why is it that no mobs are. Type /entc and see what numbers you get. And ofcourse, 4-5 mobs are spawning. Making the walls 5 blocks high allows endermen to spawn in your trap, but they will teleport away if they go into the water stream, so that's more lost mob spawn opportunities. I made a copy of my world and went into cheats mode to see if they would spawn more if I killed everything else like normal piglins and hoglins and things like that. Original Description. Otherwise make sure you check the bukkit. 8>1. Evokers are a hostile mob in Minecraft that only spawn during certain occasions. I have a mobgrinder with light level on 0, so hostile mobs should spawn but they dont, I also have a 20x20 area with grass for passive. The mobs spawns specific to those structures would spawn as normal. My only two problems now are magma cubes spawning, but I don't really know of a way to stop them from spawning without stopping pigmen also. I fly over to the outpost a couple hundred blocks away. Why aren’t mobs spawning on my XP farm? The hostile mob cap in the single player game is 79, and if that cap is met, no more hostile mobs will be spawned. And don’t go further than 128 blocks in a circular radius in Java edition and 56 blocks in Bedrock edition. While building a farm in the Nether can get risky, blaze rods are a necessity for the end game, which is why this farm basically kills two birds with one stone. Every witch hut spawns a witch inside during world generation. CryptoBecause we were close to the world spawn i thought maybe the spawn chunks are the problem so i built the same farm far away, didn't work either. Look at the Farming topic of the Zombie Pigman article at the Minecraft Wiki. Remember that light level needs to be 0 for mobs to spawn now and light can shine through things like slabs and stairs. From the drop, let them wander into a water current which then moves them horizontally into your holding area under a two-block ceiling. Ranged weaponry is. 3. 1% per level from the Fishing skill +0. i use a lower level of scaffolding (doesn't block spawns) and an upper layer of water to push mobs. It's the height of the afk platform that's the problem, mobs won't spawn if you're too close to the spawning area. The amount of mobs in a dimension is limited. Since the space under the slabs/trapdoor is a 1 block space, nothing will be able to spawn there and baby zombies shouldn't be able to escape. Check for entity counts in all directions and make sure that there are no ender-men spawned anywhere outside your farm. Also, it is definitely dark enough for mobs to spawn. 3 Answers. Another reason can be, that your waiting-room is too close to the spawning-platform and some of the possible spawning-spots are blocked by you. You need to remove all the water outside of your farm to a distance of 128 blocks from your player (the distance at which mobs stop spawning). A link to his YouTube Channel is in the comments if you want to checkout his other builds. If you've move it up ~13 blocks but didn't move your pickup spot, you are probably too close to the. Ngl theres a lot of problems with the farm but the mains one are theres not room for mass amounts of mobs to spawn and also theres light. Once the player places down a wall that is a "player placed wall" were no mobs will spawn. Second, you need to be at least 24 blocks away for the mobs to spawn. 16 nether update the nether is divided into various biomes with unique mobs spawning in them. I did the /kill @e command once because there was a lot of mobs on the nether fortress, the difficulty was only on Normal but there was like 100 mobs in the nether fortress so I am forced to /kill @e. There might 2 possible reasons: Not enough torches around the mob farm. witch can spawn and have quite a decent amount spawned sometime. You could do it by hand, but minihud or bbor are always great tools to check spawning spheres. No other spaces for mobs to spawn. So now you will have 10 zombiepigmans and your friend 30. Another problem could be that the grinder is within 128 blocks of land/caves, so. 420did69 • 1 mo. Maybe it is interfering with Phosphor mod (or vice-versa). The Evoker is a mob in Minecraft which falls into the category of Illager mobs, a group that acts as the opposite of Villagers. My farm gets the zombies outside of the 9x9x9 spawn area quickly, so I don't think that's the issue. If I'm seeing this correctly the water in the right tower gets removed first. I have a gold farm that works a little differently to yours, here is a rough plan:I tried about 5 different Creeper Farm designs, but couldn't get them to work on the new 1. For example, the Ender dragon is a boss mob, a sheep is a passive mob and a creeper is a. The mob spawner can get only up to 6 monsters within that area, so if that mob cap is reached, the spawner will stop working and won’t spawn any more hostile mobs. If there's still endermen anywhere else in the end, you won't get spawns. This is also the case for monster spawners. They start spawning again only if I kill the ones it already spawned. Hello, I needed a form of. 20, it simply just doesnt work. So, I've found a dungeon spawner in my survival world that spawned skeletons, so i've decided to use it to create a xp farm. From stephenled7's comments it seems like that is not the type of farm he has built so I would not suggest standing within 16 blocks of the farm as that will prevent spawning in the type of farm I believe he has builtGrapple to the ceiling will make mobs spawn. but now after putting it back to normal, we noticed mobs don't spawn anymore. Start off by building a “plus” shape, with each line being 2×8 blocks wide and a minimal 2×2 gap between them in the center. I even limited his farm to three floors, which is what I have, and he is still getting so many mobs. A village center is the northwest bottom corner of a point-of-interest (POI) block, which can be a bed pillow, bell, or workstation. Slows down my farm immensely. Many players try to use something other than trapdoors inside the mob spawning area, resulting in mobs not falling down into the killing area. Make sure it is actually a full 2 blocks tall. Typically the inconsistency lies in the way mobs leave the water and fall downwards. Background: I built a small mob farm using dreadful dirt and a few other bits from Mob Grinding Utils plus redstone-controlled lighting using SImply Lights's blocks. Look up hostile mob spawning mechanics for more info. Basically if there are caves below then mobs will spawn there and count towards the limit. (Java feature) If your afk area is within 24 blocks of the farm or beyond 128 blocks (or 44 if you are on sim distance 4) no mobs will spawn. Rather than attacking you head-on, Evokers can summon vexes to deal damage. Drops. You can build the farmer on the ground but only if you lit up all the caves and dark spots in a 148 blocks radius. You can improve the spawn rate but it's a lot of work. For each player that is currently online, there is a valid spawning area around each player. As long as nothing can spawn on top of the spawner, you should get the same drops. before this, it has been about 80-100. If you keep an eye on your farm, you will notice a vast difference between when there is 5 players online, and 20. We should be able to stop them from spawning by having the water source be a waterlogged block instead of an open water source. The mob cap in question is for hostile mobs specifically but the F3 info doesn't tell you what kind of entities it's detecting. By Safety box, you mean the area with the honey, chests, etc, and that area alone right? Just making sure. Then place two cobblestone blocks on top of that one. Evokers are a hostile mob in Minecraft that only spawn during certain occasions. 9>1. The design is simple, when the skelles spawn, they fall into a 2-block high water current (they don't have ANY way to receive fall damage when spawning in the room), which goes to a single direction to another current, which brings them to the water elevator. It won’t completely fix the problem, but make sure the tops of the obsidian pillars are lit, or otherwise spawn proofed. Any non-solid block is considered transparent (slabs, stairs, glass is also considered, trapdoors, chests, etc. This is a very fiddly technical rule of vanilla that doesn't have anything to do with modded. Mob Spawner for XP isn't giving me a lot of xp. Why aren t mobs spawning in my XP farm? Many players complain about mobs not spawning in their farms. You have to fly very very far away and back to get them spawning again. After doing some research, I still can't understand why they aren't spawning. When I played on a massive semi-vanilla server for a few months, I was the only one with a semi-functional mob farm because I dug out every chunk in my claimed space and filled it with mob spawning platforms beneath ground level (something like 12 chunks). Raickyy. Look at the Farming topic of the Zombie Pigman article at the Minecraft Wiki. You need a huge perimiter to make it work or build high in the sky above an ocean, to reduce the natural amount of close-by spawn-chances. XP farms are semi-simple, find a mob spawner, put water pushing it into a one block hole, maybe in the middle, and then look up the specific mob to see how much fall damage makes it half a heart point, and then make a drop that big with a one wide hole there and punch them :P. I had used the Mekanism boxes to bring a bunch of spawners back to my base for a. so usually you see people building their farms at y=127 above a large body of water to improve rates (this is a good idea because it keeps you and the farm in a bubble where everything can spawn and not despawn, and. The F3 menu will allow you to check various stats. 16 nether update the nether is divided into various biomes with unique mobs spawning in them. We're in hard mode but often times mob farms are empty and our guardian farm won't spawn despite waiting fifteen minutes. Mobs do NOT need a spawnable surface (block). As for hostile mobs, unless you are on a server I can't really think of any reason why you aren't seeing any mobs; even if there happened to be a lot of caves you'd still see them on the surface at night since they prefer to spawn in flat open spaces due to the pack spawning mechanics, plus I see plenty even with the size of cave systems you. Just be careful when going in the spawner to check the lighting in Survival. The cobblestone one, where you build up really high and build an enclosed room and place water buckets so the mobs fall down. All crystal spawn sources are multiplicative. U have to spawnprof a Area of about 6 Chunks in every direction. But someone on reddit told me in realm for mobs to spawn player needs to be 24-42 blocks away and i thought im playing multiplayer so that. Sorted by: 2. Prevent mobs from spawning underground. If you have messed around with /gamerule, make sure that doMobSpawning is true. As has been stated in comments above, very likely many of the mobs are spawning in other areas. 16, but the villagers aren't getting scared and the zombies aren't attacking them even if I place them in the same room. 3 all that well). Step 2: Widen the space and begin the set-up. No I am not on peaceful. A trident killer is a red stone machine that moves a trident in a way that it hits mobs. They can see you at your AFK position and will inform freshly spawned pigmen that you are to be attacked. You can also make the soul shard spawners. 1: there is almost no space for mobs to spawn. Mob spawning in bedrock edition is a. Otherwise, it tries 4 times to place the mob at a random position within a 8 x 8 x 3 high area centered on the spawner block's lower left corner. So I built a very basic mob farm. The world generation mob spawning rules check the available blocks by height, starting at bedrock and working up. 16. its definitely the problem if you arent doing that. when done building the mob farm it works. I have recently built a zombie pigmen farm for 1. 16. Needs to be a lot larger. This will increase the farm’s spawning rate. I'm talking about the other mobs filling the mobcap. In Bedrock, the cap on the number of mobs is lower which basically means that there can't be as many mobs in your world. I don't know what to do, I spent an hour building this and I don't want to have to redo the whole damn thing. ago. #1. 5 and i updateed it from 1. This limit increases depending on the loaded chunks, so more players in different areas raise that limit. This gamerule, if false, will prevent any mobs from spawning. Even for flat plains, surface is typically around Y 65-70, which means you need to be at around Y=200 and your farm built accordingly. So, according to the information you have given, you are doing everything correctly, and Notch is simply not smiling down upon you. I am in "hard" mode and I have built at the height limit (or one block below). ago Ngl theres a lot of problems with the farm but the mains one are theres not room for mass amounts of mobs to spawn and also theres light. Fishes are one of the easiest mobs to farm in Minecraft. All mobs outside 32 blocks don't pathfind. I have found that mobs other than witches are spawning in witch huts. Remove the walls in your safety box. I have 2 cave spider spawners almost right next to each other but one for some reason does not spawn mobs. A spawner will spawn mobs. Or remove the stone bricks and replace the slab that you broke with a trapdoor. make the channels wider on the lower half, 4 wide then 2 up top. I downloaded a X-Ray texture pack to see if there was anything wrong inside the box, but there wasn't anything causing a problem. The stone slabs are placed as seen, and in the layer below you can see a test I did with carpets being placed in a 3x3 square pattern, covering each corner, and neither technique has worked. Spot 2 is far enough for Drowned to spawn, but it's too close to caves underneath where other mobs spawn instead, and don't despawn easily. Bot. To get the creepers to spawn only in your farm, you will need to light the other accessible blocks where any mobs can spawn in a perimeter distance around your farm. Meaning you're going to need 24 buckets of water to make the cross. The most challenging part of the process is finding a zombie spawner in Minecraft. That isn't going to work well because other mobs are going to spawn around it making your farm much less efficient. . Place the Monster Spawner. This can be done by exploring. You will need to stand back away from your witch farm to make any progress with it. Short answer: Iron golems attempt to spawn at the "village center", but due to the current setup there isn't room for the golem at this point. Vanilla Minecraft, no mods, standard (no spawner) mob spawner design. So recently, i made an enderman farm in my 1. If you are only around Y=130, potential mob spawn area goes all way down to bedrock. Also remember that hostile mobs will not spawn within 24 blocks of a player, and will instantly despawn if the player. If your AFK spot is correct and you don't play on the server (where ghasts would despawn when anyone else is in the overworld) and you are not playing peaceful, then you definitely should get some ghasts. Since you're so high up the rates will be very slow with such a small area because most spawn attempts will fail. CryptoA 9x9 room centered on the spawner with 2 blocks above it will give the maximum amount of spots for spawning monsters, whether they are spiders, skeletons or zombies. 32 blocks isn't really high, for maximum effect from the torches you want to light up as many dark spaces, including caves, as possible up to 128 blocks away from where you are standing. It’s likely that endermen are spawning there and teleporting to the grassy area. Any. The “plus sign” with multiple floors and something on the edge to trick the mobs path finding? These farms are very inefficient on bedrock. SMP Mob spawn issue . (I am standing in the center of the farm in y=3) The platform is made of iron blocks. One thing that may increase you luck is lighting up the slime farm in some manner. This will make it so mobs can only spawn in the farm. It'll average out to the same number of mobs per chunk, but one player may have more mobs than another. GameStop Moderna Pfizer Johnson & Johnson AstraZeneca Walgreens Best Buy Novavax SpaceX Tesla. It relies on portals as an elevator, but it does not use portal spawning. Build farm lower - lower farm means lower subchunk, which means the game checks less blocks to spawn mobs light up caves - mob cap is held up by mob spawns within a 128 block radius around the player Increase spawning spaces in farm - increase blocks that mobs can spawn on. We use science, demonstrations and experime. I've just recently noticed that after about a half hour of waiting, I only managed. No. The game randomly checks places to put mobs and since the outside is much larger than your trap, most of the zombie pigmen spawn there.