how come you can still answer someone's questions on here, even if they have temoparily disabled their account?

Because the post is still there and they can read it if they return, and interact with others who are still active in the comments.

It applies only to their profile.

Sort of a hold over from a few years ago. Where you could still respond to a post, from the groups, after the original poster deleted it.

It still doesn't really get deleted until after six months. You must delete it from your settings to really delete it.

Why not?