If your family had over one hundred billion dollars, you would also have an underground bunker that would make any Roman Emperors palace look like a housing project after the niggers were allowed in. It's only common sense. Something bad can always happen, and it doesn't hurt to have a place to run to just in case. And once you get a certain amount of money, how much more you have doesn't make any further difference. They could not possibly spend all of their money in their lifetimes. But for a piddling couple of billion, they can ensure that they live out their lives in the manner to which they have become accustomed. It's simply insurance.