Interestingly, America is one of the best places to be if you are wealthy (part of the motivation on this thread). So it's also unlikely for a wealthy American to move.
Believe it or not, a lot people, in poverty or otherwise, really like the unique things in this country and most would rather have it this way than to move to Europe (which has its own share of major problems despite being a cool place overall).
Also, poor people rarely know the reality of other countries. I have friends in the States who firmly believe that Europe is a hellhole even though they are literally a medical emergency away from a bankruptcy.
Maybe that is because they value something more than Free Healthcare. Maybe they are not willing to trade this liberty for the safety of government services.....
Hmm Actual Freedom of Speech (we are not putting people in jail for jokes on YouTube as an example), The right to Self Defense (aka 2nd Amendment), the relationship between government and the people (i.e we believe rights transcend government and are not granted by same), I could go on and on
Believe it or not, a lot people, in poverty or otherwise, really like the unique things in this country and most would rather have it this way than to move to Europe (which has its own share of major problems despite being a cool place overall).