Earlier quoted context omitted.
He's still relatively young, and likely realises the near absolute power he holds over one of the largest companies in the world is not something he can get back once he gives it up. Also Gates, to put it in very uncharitable terms, has shown that it doesn't matter if you're seen as a hated, greedy CEO as long as you do enough philanthropy later in life.
What would Bill Gates have to do to finally shed his reputation as a business man? Honestly, Gates seems like a pretty good guy from interviews he’s given and he’s doing something good with his money.
So yes - Gates seems like a pretty good guy. And he'll have paid a lot of money to create that impression.
Zuckerberg doesn't seem to be running the usual PR operation - possibly because he's too young to be bothered, and possibly because he doesn't really care much.
Likewise Bezos. But you can be sure that if/when they turn to philanthropy, they'll consider the option of a similarly wholesome transformation and proceed if it seems likely to provide extra social leverage.
The alternative will be managed media invisibility, which is also an option at that level.