I'd argue they are far from some of the smartest people in the world. Smart? Sure, some (many?) but I've known quite a few idiots in software. But I'd hardly compare the regular software engineer at a FAANG to some of the geniuses in the world.
But they put up with it because it's a career and not a job. Many of them couldn't handle a minimum wage or working class job. No breaks, short lunches, no wriggle room for life, permanent fast-tracks to firing.