For some reason, when generating my biome, none of the mobs that I put in there will ever spawn, though sometimes default vanilla animals I haven't added will. I've tried generating my biome in a single biome world and the mobs I desired spawned but it needs to work for a default world preset.
This is the json file for my biome: https://gist.github.com/Phoenix-WB/e6499a5e5e660d5d4435262f32e61e41