[Tyhm]

Why do Dievils carry keys anyway?
Why do they drop hands when they're all feet?
Why do strange keys appear when rooms are cleared?

It's a game. I dig that as an online game chests are a bit weird, but it would be hypothetically possible to have a chest from which everyone is entitled to take something only once. Why not, we've already established the existance of magic.

It'd make more sense if Yetis were big, mean, hard to kill, and didn't give a great deal of experience (to keep hunters from taking too much of an interest) and, if you don't have the weapon/armor/whatnot dropped by them/if you don't have the flag indicating that you already picked yours up at one point, when you kill one it drops a weapon/armor/whatnot, possibly locally.

That or they just randomly drop massively powerful upgrades that hunters can sell at market to weakling newbie miners.