Sounds like his net worth was over 100M at the time. I guess past a certain point, you’ve got enough dividend stocks and want to gamble on something more exciting.

yeah, also 5m out of 100m is nowhere close to an all in. There's a good chance he just had it lying there amongst a bunch of other stocks he was gambling with and didn't even think much of it.

Yes, but if you had $100M you could retire and take some risky bets.

His stock was worth $320 million after the IPO, and he let it all ride. On a single stock in a two-year-old company. Nobody could afford to do that unless losing most of $320 million wouldn't affect their lifestyle. Being wealthy explains most of it, but I suspect being 72 years old was a factor, too.

Some jobs are not just about getting enough money to retire, they can also be about making the world a better place (or sometimes just believing that's the case), just living a passion, just having a social activity and many other reasons.