Zombies spawning in the Nether

I removed all mobs from the nether wastes biome except ghasts and zombie piglins, for some reason regular zombies are now spawning there too.
minecraft:dimension/the_nether.json
{
  "type": "minecraft:the_nether",
  "generator": {
    "type": "minecraft:noise",
    "settings": "minecraft:nether",
    "biome_source": {
      "type": "minecraft:fixed",
      "biome": "minecraft:nether_wastes"
    }
  }
}