It's most likely the case that there are multiple different bottlenecks. It's not just 1 person in a room somewhere saying "we need to make protect the elite!" - it's more likely just a lot of people continuing the status quo and few people fighting the change it.
> The AMA pushed for limited residency slots ~20 years ago, as they feared too many doctors would cut their own incomes.
For some reason, residencies are paid by the federal government. Not sure of the history there - I find it hard to believe a resident doctor is a net-loss for the hospital system. Either way, I can't find any legal cap on number of residents - only a cap on funded slots (ie, a hospital could hire more residents and pay them out of pocket).
What I can't quite figure out is patient outcomes... morbidity appears to have increased (very slightly) as resident working hours were reduced (possibly more risk from handoffs than tired MDs?) - how does the EU compare in this regard? Somebody must have done a study...
Anyway, some form of on-the-job training seems reasonable here. But the current residency system in the US definitely appears broken, for several reasons.