I think that the key difference is that plenty societies were built with the “immigration” mindset. It isn’t just the ones in USA, but mostly the whole New World. And even if the “bulk” of the immigration in the XIX and XX centuries is over, the mindset is still here.
As opposed to the typical society in the Old World where, if you were born somewhere, odds are that your grand-grand-grand-grandparents were also born there, like Japan and UK-minus-London.