Or is it that there just aren't enough native applicants (like grad school) ?
However, some usa grads do not match to a spot, around 1%, which makes lots of US educated doctors (rightfully) really mad. You get random foreign doctors going to state sponsored schools with openly nepotistic admissions sometimes getting spots over people who trained here.
Imo the solution is more us medical schools opening, which is slowly happening. It is however not so easy to do so due to the (rightfully imo) high requirements.
But yes, also a small number of people just don't have the intellectual ability to handle it, although schools do a lot of screening to minimize this. Graduation rates at schools are typically 100%, with maybe 1 person every other year failing out.
Foreign medical graduates who scores above 65-70th percentile have no problem getting into residency programs (I've made a comment above with more details as to how I know all this). For a green card holder, you just need to get ~60th percentile of the USMLE score (which translates to about 240+ in step 2 CK and step 3 USMLE scores).
All I wanted to say is that the bar isn't too high for a US citizen to get into a residency. That doesn't mean though that the path to get into residency is easy. It is extremely convoluted and requires a lot of persistence and planning. That's where (along the way) people fall through the cracks.
And there are more empty homes in the US then there are homeless people. Should be a no brainier to solve that to, right?
It's not as simple as the number of slots. In the SF Bay there are only a couple dozen family medicine slots every year and they all get filled but programs in the South and the Midwest leave spaces open on every scramble.