Most countries don’t tax citizens living abroad on foreign revenue, and just forget about them once they become residents elsewhere (unless they still have income from their country of origin).

And by most here, you mean every single country in the world apart from the US, Eritrea, Myanmar and Hungary.

Hungary does not tax it's citizens living abroad.

I was going by the table at https://en.wikipedia.org/wiki/International_taxation#Individ... but it’s entirely possible that it’s incorrect.

It looks like Hungary technically taxes nonresident citizens except in almost every case where it would matter.

That's pretty easily dealt with through residency thresholds. We do this in the UK, counting people resident for tax purposes if they spend more than so many days in the UK in a given year. I would be very surprised if the US doesn't already do this to determine non-citizens tax status.

That's how state taxes are dealt with in the US and a number of people go to great pains to make sure they stay exactly the number of days in some high-tax state that lets them skirt liability. I'd be surprised if similar things didn't happen in Europe but I don't pretend to be as familiar with what goes on there.

Sure, people definitely skirt around the edge if the rules. They’ll do that wherever you set the thresholds though.