You have people that have gone through the ringer to become doctors. These are the type of people that when you say jump, they ask how high. You can pretty much get them to do anything you want... because they are self-selected to be that sort of people otherwise they could have never become doctors. So when a manager comes to them and tells them they have to work so and so hours, they do it. And they suck it up, because that's who they are.
Even though I've suggested other motives in play elsewhere, you are probably on to something.
Most doctors become doctors either as a childhood dream or to fulfill the expectations of others. Lots of pressure at an early age - and it only intensifies from there. Getting the grades, pre-med maybe, certainly biochem, then med school.
Residency is the home stretch to a lifelong commitment, feet don't fail me know, brass ring almost within reach...
Demanding perhaps, but not questionable. It's just the nature of the industry. Not an apples-to-apples comparison, but look at combat medics for contrast during wartime. There are limits to what humans can do, but the 120-hour workweek in a heated-and-cooled hospital does not bump into those limits.
Maybe it would be 'better' if that wasn't the case, but it's simply what is.