If you start and retain ownership of a company that is one worth day a billion dollars, you're a billionaire.
That doesn't mean you have a billion dollars in cash. It doesn't mean you have a billion dollars in hard assets. It means you built a functioning organization that is performing some valuable service in society, and some accountant has associated some value to that entire organization of more than $1,000,000,000.
At what point do you think founders should be punished for that accomplishment by having some of their ownership stake taken away from them?