Because billionaires accumulate wealth through assets and unrealized gains, many of them skip taking a traditional income and pay. If the numbers in the links below are to be believed, according to paulgraham's calculations, this might bump them into a ~fair range (when comparing to average/median earners).

https://www.nber.org/papers/w34170 https://www.propublica.org/article/how-we-calculated-the-tru...