Once you already have money it can be wise to move to another country (one that does not heavily tax retirement income, for instance). The US has no double-taxation treaties with many countries, meaning that if you are paying taxes in another country, you will not have to pay US taxes (up to a point, last I checked it was around $105k you could make before needing to pay US taxes).

Now imagine that you have also moved to a wonderful country that also has a lower cost of living in general. So you find yourself in a position where you are paying far less in taxes, are still able to collect social security, and everything (except possibly housing) costs less. It’s a way to give yourself a lifestyle that you wouldn’t be able to afford in the US. If you add to that, if you move to the EU, you will probably end up somewhere walkable that also has cheap and easy access to a bunch of other countries.

Why wouldn’t you? I know there are people that can’t imagine living outside of the US, which is something I have trouble understanding.