Feet are awkward and it's just easier for a second person to do pedicure services because they can get to every area of the foot. That's a huge advantage of a professional pedicure.
I've heard of people doing a home pedicure, usually when they get some friends together and they do each other's feet. This is fine for people who don't mind the whole "foot" thing. Some people are really grossed out by feet, though, so they probably need to get their pedicures done by professionals.
I've tried to paint my own toenails and it can get very awkward to get to all the toes on both feet. I'd rather have a pro do it.