They've done those studies and context switching has historically been where the most problems occur. Whether they've repeated them with modern electronic medical records and systems, I don't know. I think most people agree there's probably a better middle ground between 8 hr shifts (3 handoffs a day) and the standards set by a dude who liked to experiment with coke and meth.

One of the big issues that I feel like doesn't get touched on as much is longer shifts allow less doctors, which reinforces the artificially low doctor graduation rates. The national board in the US pegs the graduation at X thousand new doctors every year and that number is mostly tradition / vibes. No we don't want to compromise on the ability of new doctors, but "gestures vaguely to US healthcare" good lord do we need more of them. Much the same could be said for nurses.

And all of that circles back around to not wanting to dilute traditionally higher paying job markets with more practitioners because the for-profit system will try to wring out every cent they can.