The excuse I always hear is that if they don't work that hard, they'll get fired and replaced with someone who does. I'm sure that's true for some jobs, but a) it's likely very few of them, and b) why would you want to work for/with people who have so little respect for you and your health in the first place?
Sure, promotions might come less often and raises might be smaller, but that's a trade off you can consciously make: more money, or better health and family/friend relationships. And you also set an example for your peers: if they start complaining about their health or about burnout, you can show them that it's a problem that can be solved. And the more that people do this, the more people will realize it's possible and the right thing to do.
And yes, there are some who live paycheck to paycheck, hold multiple jobs, will take any job they can get, and don't have much choice. I'm not talking about people like that... though that is another conversation that should be had more often; no one should have to be stuck in a situation like that, but so many are! And yes, there's unfortunately sexism and racism involved; I expect women and POC will get looked upon less favorably if they set stronger boundaries than white men will. But I don't see that as an argument to destroy your health.