Well... you can get it.. but you'll have to work at it (a custom kernel that supports either the Layers or CyanogenMod theme engines and said themes). Google keeps dabbling into dark modes in the UI, but I think things just start to get messy... they've been trying to make the entire interface more consistent over the past few releases and tossing in a mode that, literally and figuratively, tosses the aesthetics on its head must not be worth the trouble.
I mean, I've played with a lot of the dark themes that are available with either Layers or CMTE and most of them make a mess of things.