The paintings are assets at least valued somewhere in the realm of what he paid, and his income is no doubt hundreds of millions per year.

And remember, just because he spends $500M on something we'd spend $500 on, doesn't mean everything in his life is proportionally expensive. His Big Mac still costs $5 just like everyone else.

Even if he spent 10% of his money, the other 90% still equal $4.5B, which is more or less infinity in the real world. I'd be shocked if most billionaire even spent $100M/year.