> They likely already had healthy pile of cash and stock.

True for every billionaire too. They have so much money not only do they make it faster than they can literally spend it[0]. They have so much money their great grandchildren never have to work, even if they procreate like Musk.

For many people money is not about how it can be used to buy things to improve your life but about the social status that that wealth gives you. Take Musk as an example. He cared a lot about becoming a trillionaire. But even a billion is an incomprehensible level of wealth

[0] on a 5% interest account you'd make >$5k/hr or >$4m every month. Literally the time it takes to spend your money will allow you to recoup it. E.g in the time it takes to buy a Tesla you'll have earned more than a Tesla costs. Same even for supercars, which take longer to buy.