Then why do they keep pursuing more wealth? If you like money primarily for the pleasure it can buy, why not spend more time enjoying it? Why kill yourself just so your descendants can be financially secure?
Anyway, if you have the personality that creates a company like Amazon, you can't just sit back and enjoy it. It's just not in your nature. I had an uncle like that - he kept starting companies long after it mattered financially. He'd sell the current one, tell everyone he was retiring, sit around miserably for a few months and then start another. "It's mostly just a hobby," he'd say, and sell it for ten million dollars a few years later and start the whole process over.
Also, flooding your descendents with money isn't necessarily a good idea. People who grew up with more money than they could ever spend tend to be pretty unhappy. Warren Buffett claims he left his children enough money to do "anything they want to do, but not enough to do nothing." The rest he gave away.