It's interesting to note that American Presidents never go back to private business after their terms in office. They typically become writers, philanthropists, or take up positions at Universities or honorary public sector jobs. But never has a former President become the CEO of a business after their public service.
And that's not that new a thing, they didn't even before the age where it would be impractical from a security perspective. I imagine it's hard after being dubbed “leader of the free world”, to being anything other than “former leader of the free world”.
Extra bit of trivia: the last president to retire to the now-antiquated job of “gentleman farmer” was Franklin Pierce.