The AMA orchestrated the capping of residency slots through CMS/Medicare, which is the primary structural impediment to increased supply. Doctors in the US make integer multiples of what they do in Europe in part as a result of this.

I have to say: you can go either way on the AMA, I guess, but it's a weird hill to die on, isn't it? They're a trade group, not a public health organization. They exist for the benefit of their members.