I'm afraid the stick-with-your-team thing only applies to fans - the star players move around to follow the money, or their contracts are traded off by the owners.
It's an odd blend of big business and tribalism, and other things get caught up in it, like fascists using football hooliganism as a stomping ground and a recruiting ground, and that gets linked to particular teams at various times.
Latest thing now is the English team has been warned that, if there's any more trouble from the fans in Belgium, they are likely to be excluded from the competition, which would really make the shit hit the fan.
Meanwhile, so far as I've seen, there's been no significant trouble in Holland, taking us back to the opening post in this thread. And some of the countries who've been playing their games in Holland have fans with reputations pretty well as bad as the English.