These billionaires got where they are because they are good at what they do, and also because they enjoy it. I don't think it is any different than singers, musicians, or artists who want to keep doing what they enjoy for as long as possible. Who's to say that, while working, they do not also enjoy some leisures like travel, good food and drink, the opera, the arts, and sports, etc...?
If I could make loads of money the way they seemingly are able to do so easily, I would not quit either.
PS. Ah, I just thought of one thing I can do that the above men could not do. They could not take off for more than a month for an RV trek while staying incommunicado.
But then, many retirees here say that they would not care about RV either. So, what is it that a retiree can do that these billionaires cannot?
"Old age is the most unexpected of all things that can happen to a man" -- Leo Tolstoy