The way I see it, leather and bones come from "monsters" and meat comes from animals. A normal pack of wolves or rats would run away from a combat party, and the rats shouldn't be a threat to even a lone, unarmed, baseline human.
Viewing post in Mod Idea: Hunting/Mining Overhaul.
I mean deer are a rather large animal that people get meat from and they also use Buckskin for leather, and the natives at least, used to use the bones for buttons and tools as well, so I can get where you wouldn't always get meat where you get leather but no matter where you get your meat you will get hide and bones.