You mean they hire accountants to do that for them? Being wealthy doesn't make you smarter with your money. I won't become better with my money if my salary is doubled, tripled or if I build a time machine and go back 37 years to buy Apple stock on it's IPO (happy belated birthday Apples IPO),
As to why billionaires are billionaires, no it is not because they are as a rule better at handling their finances. Heck, there was a report back a few years ago that found 40% of billionaires got there by either inheriting the money, or by reinvesting inheritances. In both cases, it probably had more to do with advice from a well paid financial advisor than their own ability to manage finances.