To be clear: It’s because they’re still being paid very, very well.
The top paying tech companies are kind of a weird bubble because they pay so well on average but they also have a huge upward range beyond that for top performers. It leads to situations where someone can be making $200-300K per year but end up feeling underpaid because someone they know is getting $600K for being a top performer at a top company.
It’s also important to put it in perspective. Relatively few engineers work at these companies in total. The vast majority of engineers work at more mainstream companies where the pay is still good (though maybe not retire early good) and the hours are reasonable. People at the big companies are working long hours to compete for those few coveted top positions and top salaries. But you definitely don’t have to work at those companies.
FAANG and a few fintech operations pay the big USD. The lower bound on FAANG senior software engineers is apparently above or barely overlaps the upper bound for other massively profitable companies like Intel. So you can't even achieve FAANG comp most places unless you a department director.
Also a lot of their income was stock and share bonuses, great if the stock price is constantly going up and they're growing hand over fist, but when things slow down that non-guaranteed income is the first thing to be looked at - if it's not on the contract it's not guaranteed. Sure you might be lucky, but in my experience the "Buy your house in cash of FAANG" for a mid-level engineer gravy train seems to be over if you're not already sitting on the options.
Plenty of people want to earn that extra renumeration even if it means doing grunt work or giving up on their work-life balance.