There was another possibility, they were eating mutant creatures and those affected by sunlight, often diseased, knew they wouldn't live long, and wanted revenge.
After all, the people at the base were not mutated, and they had various types of food and water to cope with the apocalypse, which made those outside feel resentful.
Initially, these people enjoyed life outside, thinking the apocalypse would soon pass, and afterwards, those who dominated the hills would become regional tyrants.
And they believed that once the extreme weather passed, they would be able to farm and have a future.
But now, the disparity had probably caused them regret and unwillingness, certainly a major diversion from what they had originally anticipated.
Anyway, the state of these people now was as if they were desperate, and it wasn't just about looting.
