Major medical organizations have been advocating for years for more physician residency spots. Unlike NPs or PAs, some residency is required for physicians to be licensed.

Right now, there are not enough residency spots for every US med school graduate.

The AMA very successfuly lobbied to reduce the number of medical schools, cap federal funding for residency and cut the number of residency slots 20-30 years ago, and we are now dealing with the fallout of that. It has softened its stance in recent years, sure, but even if we fix all of this today (doubtful because of the usual political gridlock) it will be another couple of decades before the situation will actually improve.