You make a very good point. I can do a lot of things. The problem is that I can't do them nearly as well, or as efficiently as someone with the skills developed over time. Example, when I decide to tile my bathroom, I could do it myself and the job would turn out 'ok'. OTOH, I'd rather hire a professional to do it as it will be done well and not takes months to get done.
It really is a pleasure watching someone work who is good at their craft. As Jiffy says, they make it look so easy.
That's why you hire me to do your tile work, and I hire you to do my eye glasses so I can see what I'm doing.