Different people - different needs/wants. Lots of billionaires don't spend any significant part of their wealth on themselves but rather invest or donate to charity.

$5 million doesn't go as far as you think. I'd rather have $100 million invested in a solid business that can provide for me (and 100 employees).

And some people just like working, whether the money is the goal or they like the work and the money is a side benefit. I know my own retirement goals have shifted over the years because my idea of retirement has changed.