They’re not a wholly sovereign country. We are occupying them because Germans keep trying to conquer Europe and the fundamental reason for our presence is to make sure that does not happen again.
Meanwhile, they’ve done just that economically, thanks in great deal to the US leftists who kept insisting on aiding them (originally through the American Committee on United Europe); and the same leftists helped them do that ideologically as well.
A lot of people haven’t learned history. The idea of “a United States of Europe” goes back to Kaiser Wilhelm II, and he said its purpose was to be “against America”.