Custom structures spawn entities with `/place`, but not when generating naturally.

Afternoon, gamers. I'm working on a 1.20.1 datapack that will be a compatibility patch between Dungeons and Taverns and the Illager Invasion mod. I'm a big fan of both, so I'm adding the new illagers from that mod to Dungeons and Taverns structures like the illager camp, illager hideout, etc. My strategy so far has been adding jigsaw blocks to existing Dungeons and Taverns structures that then attach to "structures" that are just illagers. This way, I can spawn from a pool of potential illagers for some randomization. This is what vanilla villages do for spawning golems and villagers, after all. I got a problem though. Everything works 100% when using the /place command: vanilla pillagers spawn and some modded pillagers spawn from a template pool I made. However, naturally generated Dungeons and Taverns structures that I have modified do not spawn my new illagers. They're not even spawning the original vanilla illagers that are just entities in the structure .nbt and not "jigsaw"-ed in. I have tested this in over a dozen generated worlds and /place always works, while a naturally spawned structure that I modified does not spawn illagers. I've made several compatibility patches for Bethesda games, but I'm a newcomer to Minecraft datapack development, so here I am looking help. I thought I was maybe doing something wrong with my illager spawn .nbts, but they look just like the .nbts in minecraft:structures/villager/<biome>/villagers.