Do they? I think exactly the opposite is true - if you ask any sufficiently wealthy person, they’d need a team of people working for a bit to arrive at a very hazy net worth number. Private stock is extremely illiquid and doesn’t usually have a good mark to market, ditto most artwork. My impression is that even most public stock doesn’t generally have the depth of liquidity to absorb a founder selling any significant fraction in a short timeframe without cratering in value.