But what do you do with tesla/amazon/etc. then? Force elon to sell of his shares? Take them? What if the price drops? Give the shares back?
It's not like he has all that in money in his bank account, it's ownership of companies, their value is not real until someone else is willing to pay.
The tax is his shares, those shares become public assets, the government and (ostensibly) the citizens finally get a say in what the hell is happening with that guy.