Point taken, but FYI billionaires don't "earn" a billion dollars regardless, it's almost exclusively because their net worth due to stock ownership makes them a billionaire.
If you bought a house somewhere cheap, and then the eyesore old factory down the road gets torn down, and the land around your house explodes in value, you did not make a million dollars in income, even though your house is now worth that much.
As well, most billionaires live off money they borrow at stupid low interest rates because that doesn't count as income. An accountant would be able to explain in depth but that's one of the way they dodge taxes.