Time is money and your manager doesn't want to get negative indicators
People may be scared of management, but hopefully they're reasonable. They're people, too. Most have some kind of understanding that sacrificing short-term productivity is counterproductive, both in that tired people make more mistakes and worse decisions, but also fed up people leave (super expensive and inconvenient).
Of course, your colleagues matter here. If they fail to set similar boundaries and expectations, one person isn't going to fix a dysfunctional environment. That's why it's important to work with professionals, and not people who devalue themselves and others regularly.
being able to push back is a luxury (unfortunately) that requires coming from a position of some power. that means that your colleagues support you, or that you are in a union.
where the GP is coming from is that mostly, this isn't the case.
