The way all these billionaires have built up their wealth is by retaining a certain percentage of stock in the companies they built, and then the market cap of these company got into the billions and sometimes trillions.

Let’s assume a founder has 10%. There are two options to prevent them from becoming a billionaire. Either that company cannot grow past a 10 billion market cap. That would destroy retirement for most normal Americans. The other option is to force the founder to liquidate to pay taxes. If so, then yes, they would stop further building out these companies at a certain market cap once they have no real stake or say in them anymore. Why would they work for free once they are at the limit. I wouldn’t and I think almost nobody would.