Americans are losing ground in nearly all sports. they are still the no.1 sports nation but they have really lost some of their dominance in sports over the last decades.
Just look at tennis, boxing and even american sports like basketball and baseball. of course they are still the no.1 in basketball and baseball but they have lost some matches and have to really fight hard to win now while they were just toying with them and sending the opponents home with 40+ points without even trying.
I think the problem is that america is a wealthy country. most of the richer european countries have the same problem. if a country is wealthy the pressure to get good is not so high because they have a lot of ways to earn their living.