A lot of companies won't hire former execs that have been the center of the world, because they figure anything they could offer them is a step down and the exec will be bitter and demoralized about their loss of status. It's not necessarily an accurate perception - I know plenty of people who don't care about status and are just looking for interesting things to do - but it tends to be more accurate among the population that gets to the exec level in the first place.

Marissa Mayer is running a startup lab now, Amit Singhal is doing philanthropy, Travis Kalanick is starting ghost kitchens, Eric Schmidt is also doing philanthropy plus venturing into politics & punditry, Andy Rubin is a venture capitalist, Chris Sacca retired to Montana and occasionally appears on Shark Tank. While they may have the skills to take lower-level corporate jobs, the folks who reach those levels generally don't have the personality or inclination for it.