if you are one of the ones who is valued enough to keep their job, you are strong enough to go get hired at another FAANG. Do you actually still want to be there after the bloodbath that the follow-up round of layoffs causes?
when you start somewhere after their bloodbath, you don't have to deal with all the crap you would if you stay through a bloodbath (i.e. you aren't on the hook for all the legacy shit your team owned before it had a haircut)