I prefer having traits as a constant, an important gameplay element unaffected by difficulty. It means, among ohter things, that you don't have to adjust your playstyle even further - on any Ammochain game, regardless of difficulty, you can drop your ammo once you get MAc, on any Army of the Dead game, you know that at a certain point, enemy armor no longer matters, and so on.
It's an important bit of consistency to me.