Look this picture
https://upload.cc/i1/2019/03/27/54ptNi.png
https://upload.cc/i1/2019/03/27/j2UOK8.png
"version": "1.12.2-2.7.0.574",
forge:1.12.2-14.23.5.2815

Are you in creative? NPCs does not spawn when you are in creative mode, only their nametag is visible.

This way it allows builders of structures to position NPC's and set their spawn distances for staged progression style gameplay to prevent all the NPC's of a structure all spawning at once and rushing you as a big mob. Its also much better performance wise - as it prevents all those NPC's spawning if you are generating a world by flying around. Its also much better game-play wise as those NPC's don't get killed off by mobs etc just because you passed a structure and didn't go in.

Thanks. That's so cool.