There are very few exceptions.
Psychologists are their own breed. They tend to be more patient focused then other specialties. Talk to a neurologist or surgeon and then a psychologist very different animals. Psychologists as a whole aren’t that interested in becoming rich (My wife is a psychologist). I own a soft dev company and being rich isn’t my goal either. Making money I think is a byproduct of doing good work.
Personality types. Often psychologists aren’t entrepreneur personalities.
They could work in marketing positions to help individuals or companies generate substantial revenue through their knowledge, but they often lack the go-getter traits most entrepreneurs have.
Service based businesses make service based margins. There are only so many billable hours in a day and being a psychologist isn’t a scalable thing.