I great way to help solve this problem could be to let players scrap guns, armour, bullets, or any other things that they loot or make. For example, say I kill some raiders and loot a sub machine gun and a combat knife. Instead of selling them I could scrap the sub machine gun for it's alloy and junk and the knife for it's metal parts. Also when scraping you should not regain all materials back that were put into it during crafting.
If you want to make enemies, try to change something.