Take Mr. World’s First Trillionaire, Elon Musk. He doesn’t have a dragon’s horde, his money is almost entirely invested in SpaceX and Tesla, building things he wants to build. SpaceX didn’t IPO so he could have bragging rights with his Forbes list peers, it IPO’d because it was the most efficient way to get more capital to grow and achieve its various strategic aims—largely set by Elon and its other preexisting owners.
You can take that away either proactively by making such ownership structures impossible or retroactively through taxation forcing current ownership to sell, but the end result is the same: No incentive for folks like Musk or Bezos to use their skills on big, ambitious, capital-intensive enterprises. Control is what matters, not $.