It’s not just the cost of college that limits the supply of doctors. There is an explicit limit on how many people can become doctors each year in the US:
http://blog.petrieflom.law.harvard.edu/2022/03/15/ama-scope-...
In addition, in many states in the US you have to get permission to open a new medical facility:
https://en.m.wikipedia.org/wiki/Certificate_of_need
Often the people on the board own existing medical facilities, so you literally have to get permission from your potential competition to compete with them.
https://www.justice.gov/archive/atr/public/press_releases/20...
For example from the above link:
“ In 2006, the Antitrust Division alleged that a hospital in Charleston, West Virginia used the threat of objection during the CON process, and the potential ensuing delay and cost, to induce another hospital seeking a CON for an open heart surgery program not to apply for it at a location that would have well served Charleston consumers.”