Every <unit of currency> not in your pocket is in someone else’s. Greedy narcissists can’t stand that, they need to have it all. They don’t need the extra 500 billion to spend it, they need it so the number goes up. They need to be number one. At everything. Remember when Musk lied about being one of the top players for some difficult video game, then it turned out he was paying someone else to play for him? It’s just an ego thing, which I agree is baffling.
Yeah, but lets practice some empathy.
Starting point: money can't buy happiness.
So what to do to be happy? Extreme wealth removes most practical goals like buying things or going places and doing things. Not that you can't do them, but it's not a meaningful goal to work towards.
They have to create their own meaning, whatever that is.
A billionaire trying to create purpose for themselves can be boring, or weird. Which one gets media coverage?
Gates Foundation, Zukerberg's fitness craze, MacKenzie Scott's philanthropy, Bezos and Musk's [whateverness] are all just variations on a theme. And like all people, some will be better at it than others.
Note though, that they will do what it takes to stay wealthy because what would they be without that?