I think it's more of an issue with the angle of feet touching the ground, and not wanting to create movement animations custom to different angles. It's the same reason you won't see super high-heels as an option either.
Also, with how often people discard random wolf fangs, bat wings, horns, lumps of ore, and old potions, the ground is an absolute HAZARD for walking around on in bare feet. Just wait until you run through the broken glass of someone's blinding potion, and end up crawling around like Ray Charles in a Die Hard movie.