Let me take an instance of one villain: Arlong. Arlong got defeated by Luffy, he wasn't killed. Luffy didn't stay in Kokoyashi village either. So Arlong could have returned to his usual business of enslaving the village. He would have faced ugly humiliating words from Villagers initially, but why would it matter? All you gotta do is gang-up on them. No one in the village was strong enough to stop them.
There are many other pirates who just disappeared after being defeated. It's not like they lived their life with principle or something, they were bad guys who used to loot, cheat, and kill people. Why wouldn't they continue that after being defeated?