A major limiter on the amount of trained medical doctors is not to do with someone "deciding" to have an artificially scarce number of medical students. Two important things come immediately to mind:

1) Medical schools rely on clerkships and preceptors to deliver actual clinical experience critical for learning. These cannot be created out of thin air and often rely on access to urban centers. There is already a shortage of clerkships and preceptors. https://www.aamc.org/news-insights/so-many-medical-students-... (not my original source but the nearest to hand one)

2) The real chokepoint for creating practicing clinicians is the number of residency spots. This year there were 43k graduating MD and DO students, but only about 40k residency spots. This doesn't count international medical school graduates. https://www.medicaleconomics.com/view/match-day-2023-a-remin.... Creating a new residency program is significantly more challenging than graduating more medical students.