This is a well known and oft discussed complaint.
Here's a funny thing. See, sometimes they do in fact act like it's non-lethal. In one of my plathroughs, I botched a bunch of rolls and ended up in combat with the tieflings in the Grove prison who wanted to kill Sazza. I defeated them with non-lethal combat for roleplaying reasons. I didn't let Sazza out at the time, because I hadn't cleared the tunnel. Later, after a long rest or two, I went back to talk to Sazza and she was dead. Apparently murdered by the tiefling girl.
It's also a *requirement* to knock out a certain NPC if you want to recruit them later.
So they CAN do it.
In fairness if they were to implement it now, they'd have to do a lot of new writing and voice acting to support the new branches which would result.
Last edited by WanYao; 05/11/23 08:51 PM.