Originally posted by Menzagitat:

Bases are meant to be attacked. So it is understandable why we cannot build there.
But why trolls would not respawn inside? How would that harm the game mechanic?
I would like the troll to be able to enter or leave the cave.
Or maybe he does that?
I never killed a troll in close combat in a cave but a cave became empty somehow.

The caves are a separate instance in the game, just like the burial chambers and crypts as they are not part of the open world. Personally that's something I like because it means that resources in some areas are finite and you have to get creative if you deplete them entirely.

Empty troll cave means one of two things; either it's resident has been killed within the cave or it's a cave that spawns it's resident outside occasionally. I have also had instances where I've killed a troll directly outside and it's mate was inside the cave as well - this was probably just coincidences due to how the game spawns mobs near to you.