Bezos doesn't need to sell 100% of his AMZN to retire. Just a few points would be enough to live a lavish lifestyle.
This is a real issue though, and the same problem you're describing exists in the inverse. How was Elon able to buy 100% of the shares of Twitter without prices going to infinity? You go to private buyers and sell large blocks at a discount (or buy large blocks at a premium) to the current market value. Drag-along clauses help ensure there aren't meaningful stragglers once start approaching 100%.
Mackenzie Scott got $36B of Amazon stock and has sold $8B.
Large shareholders aren't very large. They dilute their shares over time. The Google guys have a tiny amount of financial shares of Google, while retaining voting shares.
I just don’t understand how once you reach a certain level of wealth you are functionally locked out of ever accessing it except on paper. Someone must have kept their wealth or cashed out (one way or the other) at some point. It feels like, if true, no business would ever exist more than 30 years but clearly there are many businesses that have.
Typically at those levels of wealth there is a “family office” which is just a word for “hedge fund” that’s only clients are the family. Like any hedge fund they can use those shares as parts of lots deals to diversify, manage risk and pull out cash.
Sometimes it’s even simpler, dividends can provide a significant cash flow for large shareholders.
In any case, it would be extremely strange for someone to get very wealthy and then hold most of their portfolio in cash.