I think it's more that it's just really, really hard to spend tens of billions of dollars in a lifetime as an individual. After you've bought a couple mansions in your favorite cities, a beach house or three, ski lodge, hunting lodge, and a ranch you get bored of buying houses. Same thing with cars, yachts, charitable foundations. I think that's where all the interest in doomsday bunkers and space exploration is coming from with the mega billionaire class. They are the hobbies driven by the boredom of simply having everything and still not feeling whole and satisfied.