How does this actually work? I have never worked in a medical context and am ignorant of their internals so this is a genuine question.

I _have_ been a patient going to a specialist appointment where the only doctor I saw was a resident, and I don't think I or my insurance were charged any less. So if their work brings in the same amount of revenue for the same services, and if resident often do a lot of hours (I seem to recall several years ago their hours were capped to not be _dangerous_ but are still a lot), and they're paid less during their residency than after it ... why _don't_ hospitals make money off residents? Is there some training going on parallel to seeing/treating patients which is really expensive?

My source is my father who is a physician who chairs a residency. He’s always complaining about the business analysts wanting to cut the program because it’s not making enough. My understanding is that yes there are a lot of highly paid doctors at the residency who are basically just supervising the residents so you end up in a situation where you have just as many full doctors plus the resident costs to treat the same number of people. The residency also does a bunch of non revenue generating stuff like retreats and training every Friday which hurts margins.