Pillagers can spawn directly in villages, thus killing off the villagers even if the village is fully surrounded by walls (so the pillagers have no way of getting in the village other than spawning directly in it).
This is very annoying as it renders any kind of protection built around the village useless.
1.14.3 Pre-Release 2 mostly fixes this, as patrols can no longer spawn in a well lit area, so the player can prevent them from spawning in the village