That’s my question: Why?
Why?? Because physicians organizations collude with universities and medical schools to keep the number of physicians low and pay levels high. They do it under guise of only selecting the "best and brightest" to become doctors.
I majored in chemistry, and rubbed shoulders with a lot of pre-meds in various chem classes. This was (and is) well known among the student population, and as a grad student teaching labs, I watched it in action.
Follow the money!