Because there's no "simply" about it. Go ahead, mentally walk yourself through how that plays out for the rich person. Please account for all assets and potential tax liabilities. Factor in the means of production for the rich person to stay rich, and what happens when that person is no longer a U. S. citizen. All done? Oh, forgot to tell you, there's a dozen other things you didn't even know about, but the country of your previously-held citizenship will be along shortly to helpfully remind you.
That, and where else are you going to go that is more "business-focused"? Suppose you find such a place; what trade-offs are made to live there?
Because if you're still in business, you might still make more money in the U.S. due to other superior resources available here. For example, there might be greater creative output from well-paid workers who receive basic income and profit sharing, and this could lead to better overall returns for business owners. Obviously not all types of businesses would do well, but hopefully the ones that would thrive would be businesses we're more interested in seeing thrive.
That, and where else are you going to go that is more "business-focused"? Suppose you find such a place; what trade-offs are made to live there?