5x median is enough to not worry about money, ever, yet also not so much that one can afford to waste any of it. It lets you have nice things, but not stupidly decadent things. It's still conceivable to spend all that in one year, just on ordinary consumer purchases, services, and travel.
Measuring in terms of median incomes is also a good proxy for how many full-time servants one can afford to hire and employ indefinitely without disgruntlement. At 5x, that's enough for a 2.5x lifestyle, plus a 1.1x personal assistant, and a 1.4x property manager. That kind of enough is "enough".
So no, he should not have given up after his first million. He should have stopped at around $12M instead. It's fine if he keeps working, but really, after that, it's more of a benefit to others if he spends the excess rather than investing it.