Players constantly capture enemies and question them, how to deal with it?

I’m running a campaign for five sixth level players and the bard has hypnotic pattern. Whenever the party runs into any fights with enemies who can speak, they always find some way of making an enemy incapacitated or doing non-lethal damage so they can question them later.

This always makes me have to think of things for that otherwise silent NPC to say and it feels bad to make them say nothing and “force” the party to just kill them.

Question:

Is there any smooth roleplaying way to handle this situation?