What would be the point then? Headshots will always do the most damage, so why would the AI do anything but? The AI just wants to kill you, so they wont do crippling shots because they are just going to kill you, period.
Because heads, being smaller targets, are harder to hit. Taking out an opponent's leg or arm opens them up to more devastating attacks. A character might be wearing a heavy helmet that also offers greater head protection, minimizing the bonus to a successful hit to that area. In that case, more hits that do less damage, but simultaneously reduce the opponent's ability to counterattack are a smarter option.
Beyond that, NPCs would be designed to fight in certain ways. Unskilled bandits are more likely to run in charging at the torso. Trained knights would have the skill and understanding to take a more measured approach, with each attack being more precise.
Locational damage is only good if there is a valid use for the AI. Crippling in Fallout was pointless because, again, you and they were just going to kill one another. In the end, its all about killing. Thus locational damage is pointless. Headshots only matter in shooters where each side can do it and its equally as deadly. RPGs have no need for it since the end result of EVERY battle is death, and most enemies die in 2-5 hits anyway.
I stated in a previous post that I'm more than happy to not increase damage for targeted shots. Have a head shot do just as much potential damage as a foot shot. But I want the tactical effects: stuns, knockdowns, penalties to skill and damage. I want individual armor pieces to matter, instead of a single defensive value. There is no room for smart thinking in Skyrim. Either I'm capable or I'm not. In the former case, it might take a reload or two, but eventually I'll win simply because I'm luckier with the damage rolls. I'd like the option to outsmart the enemy, to find that weak spot and exploit it. I mean, adventure stories are kinda boring if it's all just equally matched opponents squaring off head to head.