How do billionaires accumulate so much wealth?
Much if not most of their wealth is held in stocks and is taxed differently than income.
Consider Mark Zuckerberg. Between 2013 and 2019, his fortune increased by 368 percent,
thanks primarily to the 342 million shares of Meta he owns.

During that period, his declared income
— taxed at a rate of 13.7 percent, similar to that for the average taxpayer
— was much smaller than his net worth and resulted in a tax bill of $536 million.
If you recalculate his tax rate based on his wealth growth, his “true” tax rate was only 1.1 percent.
https://www.nytimes.com/interactive/2026/10/13/magazine/billionaire-wealth-tax-proposition-40.html?smid=nytcore-ios-share