Football may still be inferior to Basketball for the US. So football is not their favorite sport. From some sources I've read Americans are very much into Baseball, Basketball or American Football. So this is true. Indeed in some matches I saw not many spectators present in the stadium.

My guess was still correct, European teams would dominate the knockout phase matches and this was true. I don't think there is a big gap, but indeed many players from many continents come to Europe because the focus of football is currently in Europe. The football industry there is more developed.