It's expensive to educate any health professional. You need a lot more than classrooms and textbooks--the infrastructure of a teaching institution is more like NASA than it is like Yale Law School. That's why we're importing so many from the Middle East. Though, for some reason, they are not often surgeons...
It's not the expense that is the only problem. There are vast numbers of applicants who are not admitted to medical schools simply because they limit the number of spaces. If we had a policy that allowed every qualified applicant to be admitted to medical school, but told them they'd have to pay for it themselves, then the problem would be solved.