It's a cooler, can't really fold KK here ever.

The reason he is not calling to let you cbet your bluffs is because they are not thinking that way, they simply have AA and want to get the chips in ASAP.

Folding here would be atrocious especially given the limit. When we talk about super small ranges (and that's usually the case in 4bet/5bet spots) the spazz factor becomes really important and by folding KK here you're often owning yourself against opponents capable of shoving some random combos due to both weak mental game and lacking betting patterns.

You can't fold this in a 6 max game. Vs EP in a micro FR game you can, but never here.

There's still a fair few regs out there auto stacking QQ+ AK against anybody they perceive as a fellow reg.