Bezos's billions are from capital appreciation of his Amazon stocks. They are pending taxation, because the US (and pretty much all other countries) don't tax u

Bezos's billions are from capital appreciation of his Amazon stocks. They are pending taxation, because the US (and pretty much all other countries) don't tax unrealised capital gains, because they are not stable - during a crash Bezos' net worth would drop by tens of billions of dollars, and the government wouldn't want to have to refund the capital gains tax it took from him - and because they are hard to measure for illiquid assets - if Amazon were still a private company, it would be difficult to value. So they wait until a definitive final sale, which provides a convenient line in the sand for both problems. There is, however, a loophole in the US, where capital gains are ignored if you hold your assets until your death - which incentivises people to never sell.