The bug!

The zombies/husks/villager zombies/drowneds cannot see the villagers that inside their house. Zombies have an issue with their pathfinding. They cannot find the village doors even in hard difficulty. In older versions they attacked villages and in hard mode they could break doors. Now sometimes you can hear the breaking sound(if you spawn a zombie near a door but naturally it is quite difficult because they cannot find the door) but zombies don't know what is behind the door(a villager) and they don't break it.

So the zombies cannot see and they don't want to destroy the village.

Here's a picture: