Earlier quoted context omitted.
Craig probably did some math and found out that even if he lives to 800 years old, he will not be able to spend it all so why go nuts? This way everything is manageable and he doesn't need to report to anyone.
I'm surprised that more successful people don't do this? Is the drive that lead them to absurd success what leads them to continue well beyond needing to? I find it hard to imagine hitting $10 million and not just dropping everything and spending the rest of my life on random hobbies and traveling. Maybe that's why I don't have $10 million?
For another, inflation. What used to be a LOT of money isn't anymore. What is currently a LOT of money won't be in a few more years. And the beat goes on.
There are other reasons, but from a practical standpoint, those two are biggies.