The Bug:

All mobs will look at the Player while idle, but most "sapient" or "humanoid" mobs will also look at other mobs near them. Piglins, Piglin Brutes, Villagers, Allays, Vex, Evokers, Vindicators, Pillagers, and even Ravagers all do this. The stand-out exception here is Witches.

The video below shows this behavior in action:
WitchLook.mp4

I assume this is because witches are old, before this was made standard for intelligent mobs. Now they are inconsistent with the rest.

How to Reproduce:

1. Summon a Villager and any Illager next to some animals. They will look at the animals while idle.
2. Do the same with a Witch; they will only ever look at the player. This behavior is unexpected as Witches are "humanoid"-type mobs.