I think some of it is that he doesn't really live like a billionaire in a lot of respects, takes anti-wealth political positions (he's an opponent of California

I think some of it is that he doesn't really live like a billionaire in a lot of respects, takes anti-wealth political positions (he's an opponent of California's Prop 13, for example pointing out that he pays less in property taxes for his Malibu estate than people with much more modest properties in California), is explicitly not forming a money-based dynasty in his family (he has given his kids "just enough so that they would feel that they could do anything, but not so much that they would feel like doing nothing") and intends to give away his fortune to charity. There's a pretty good summary of his views and actions in the Wikipedia article on him.