- You do a job that is, in many cases, a company itself. Lawyers, doctors, and developers can all start independent operations since the product of their work, or the service they provide, is monetizable in and of itself.
- There is a very significant skill gap, often driven by enthusiasm at least as much as intelligence, that people rarely transition between.
Compare these fields against something like electrical engineering. There the skill itself is generally a part of a product, rather than a marketable skill in and of itself making independent work difficult. And I don't know that many electrical engineers, but I'm unsure how big of a skill gap there is and, more importantly, what percent of engineers manage to transition upwards in it. If one electrical engineer is, more or less, the same as another - then you're going to see that reflected in income distributions which I would expect look more bell curvy weighted mostly by just years of experience.