I think the reason for playing in the US is obvious. They understand English there, so the people can understand our songs. Speaking as someone, who has mainly gigged in Germany for the past twenty five years, this is a most exotic luxury. Playing in the UK, to folks, who understand every word, gives me a kick which makes me feel thoroughly spoiled. I would love to go to America too. Regrettably, the American authorities (to distinguish them from the people at large) seem hell bent on making it no easier for musicians to go and perform in their country than it used to be to get into the Warsaw Pact countries. In fact, towards the end of the Iron Curtain age, it was easier to get into East Europe to play than it is to get into the US now. It is very sad. I can't afford to go to the US, but if I could break even on a trip, I would give it a go. There are certainly lots of smashing people, whom I would love to meet and play for.
Europe is no gold mine either, but I believe it is considerably easier for US musicians to come over here to play. Long may they continue to do so. They are very welcome.