It's all about leverage. There are certainly less good and better electricians and dentists, but at the end of the day they can only string so much wire and drill so many teeth in a day at rates that are pretty much set by the market. They have some leverage if they set up a business and employ people but there are still both lower and upper bounds.

Whereas a Pro Bowl quarterback or A-list movie star is worth maybe $100s of millions to a team or studio relative to players/actors who are "only" very competent. Coders are somewhere in between.