Is it all really necessary? As an outsider it looks like letting the perfect be the enemy of the good. That, or it's just tradition / an elaborate hazing ritual.

I don't see how the ability to work long hours is necessary to heal the sick. They don't train airline pilots like this, or nuclear plant operators. What's so special about doctors?

Residency certainly seems like an elaborate hazing ritual. I believe there is something to be said for errors made when handing off patients between doctors at the end of a shift, which is why you would want to train physicians to maintain good performance even over long shifts. But in general, modern residency was invented by a morphine- and cocaine-addicted surgeon who decided, hey, I want you to undergo a grueling residency for an arbitrary number of years and you'll be a doctor when I say you are: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828946/

Sleep deprivation in the service of error prevention always seemed a bit illogical. Other professions have shift handovers

Perfect? Hardly...

The long hours are much less now, though nowhere close to pilot or trucker hours. they're trying to give the future the most experience they can while still under supervision.

It'd be better to have a 5 year residency and go back to a 3 year med school, but that would reduce med school income so not likely.