Not to mention nobody with half a brain would ever find a practical application for laying down whens there's monsters and blade wielding guards around. Enemies will need a new set of animations for striking you while you are on the ground otherwise it'll look like they are swiping at the air, not to mention if you were prone and guard with half a rain would simply plunge his blade into your spine. Long story short no moron would use it, and the one possible use for it is ambiguous at best. When do you ever find yourself in the situation where you are overlooking an enemy camp? never, you never do. Are you just going to arbitrarily go prone every time you see any enemy?
There's simply not a single situation you'd ever encounter in the game where prone is more suitable than the basic crouch/sneak. It's a LOT of extra work for little to no use.
I think your missing the point. it's mainly a stealth application and not a battle application. you wouldn't get down on the ground when people are attacking you obviously. and as far as the animations for attacking someone prone go, it'd be just as weird looking as fighting a rat.
you say "no moron would use it" but what if i needed to remain unseen, and crouching didn't get me low enough. would going prone make me a moron?
i overlook enemy camps alot (especially in morrowind). you obviously aren't a stealth player so yeah, you wouldn't have much use for it i guess.