Cannibals

[Guteck]

There is thing which causes me insomnia. Why Cannibals are so powerful? Not only their strength and toughness is high but their attack and defense is too. Are they really human? Maybe demonic blood or some kind of nanobots makes them that strong? Or maybe they are former soldiers of Holy Nation or United Cities who developed taste for their own species meat? Or maybe it's social structure is similar to that of Sparta and they are completely devoted to military arts? Also if they are that skilled why they don't use any kind of armor? Could it be because of some kind Cannibals Code which states it's shame for cannibal to use armors?

[Kamos]

Survival of the fittest and breeding like rats could help. Strong people surviving and breeding compounded over generations under a sustainable birth rate, protein heavy diet(I'd guess human meat does that anyways) and a raider culture.
They would pretty much live combat and strength. Not much time for complicated things like metallurgy though. And they'd probably mostly raid trade caravans or weak settlements where there wouldn't be much armor or advanced weapons to acquire. On top of that they live under harsher conditions than most in Kenshi due to their life choices and culture making them rugged and tough by nature.

I'd say their origin is most likely found before the rise of cities or outposts in the Kenshi world. Before agriculture or animal husbandry took any root, if animal husbandry ever becomes a thing. Effectively they'd likely be holdovers or from outlying areas that just haven't developed at all without some sort of catalyst as they've been self sustaining with a cannibalistic lifestyle.