But, if they tried to move to another country and renounce their US citizenship they’d have to pay an exit tax based on the entire value of their assets, including unrealized gains.
Sure, everything is gameable if you’re a billionaire, but it would require clever lawyers and involve some risk.
The biggest problem is that part of the way they usually game is by trying to create and promote a legal minefield by promoting footnotes in the law.
Before you get to their armies of clever lawyers, you will be inundated with rights issues from Accidental Americans and senior expats who have not resided in the US for decades. Not even from taxes as most publications seem to claim but from the far steeper charges of failing to report “foreign bank accounts” of normal banks people have been living literally right beside of for normal day to day tasks, which have been mined with things like fines that are life shattering for anyone but billionaires.
It is designed so that any such solution will grind to an halt by fostering the prosecution of those least capable to defend themselves who are earning even well below what they would in the US. It is why the US renunciation rate is at record highs in the US, because the nation of immigrants have forgot what it is to be an immigrant.
So bringing it back to the point at hand, it isn’t just that they have clever lawyers, like Charles Rettig who was literally appointed by Trump to lead the IRS, it’s that they are able to hire and influence everyone involved in the process, not just on their side, to make sure they are the last to ever be affected.