A lot of european players have trouble with the concept or possibility of waking up one morning and being traded to, let's say, Minnesota. Especially the ones with families. They all have the dream to play in the NBA, but for some it isn't exactly what it is supposed to be, so when they get older they prefer to go back.
Take Gigi, for instance. He could make more money staying here, but the money he got from Fenerbahçe isn't so bad - 1.9 million per season - and there he has stability and playing time.