I think it's even simpler than that - if you are a billionaire life is pretty good, and the only thing that can get in your way is death so it's a natural place to want to invest - it's basically one of the only problems you have left!
I'm not a billionaire, but I love my life and death/ageing is one of the few real problems I have.
I'd rather have billionaires thinking like me and investing their money in solving real problems than buying yachts and marrying/divorcing every year.