You can work an H1-B nearly to death, Elon has all but explicitly said so for instance. If they're fired it's very unlikely that they'll be able to get a new job before being forced to leave the country at which point they're unlikely to ever get the chance to come back and they know this.
But this doesn't really happen in FAANG, as most on this board can tell you. Maybe in Elon companies, but they were well known for overworking everyone almost a decade ago
