A simplified view is supply and demand. There's only like 600 major league baseball players and their average salary is 4mm. Rare group to get into. There's few

A simplified view is supply and demand. There's only like 600 major league baseball players and their average salary is 4mm. Rare group to get into. There's fewer doctors than engineers or coders. And it's not like you can jump on elance and have someone remove your tonsils. And with greater supply comes greater variability in skill and salary.