If you have a gun, are really strong, are a sapiovore, are terrifying, or have mutations that increase your ugliness, all of those will increase an NPC’s fear. Ugliness from mutations also reduces NPC trust.
NPCs won’t talk to you if their fear of you is greater than their bravery + 10 or their trust of you is less than -8. If they won’t talk to you, they will try to kill you if their fear of you minus twice their aggression and minus their bravery is less than -30, and otherwise they will flee from you.
So apparently you’re scary enough to be too intimidating to talk to, and too scary to fight, so they run away.
Giving you some difficult way to calm down fleeing NPCs is something I want to add after 0.D releases.