From my layman's perspective, I assume that certain European teams feature a few Blacks (and, in the case of nauseating squads like France, a lot of Blacks) out of some mistaken belief that the Black players are actually good to begin with, or any better than the available White players.
In the case of the USA I think the placement of Blacks in soccer is not so much an extension of the belief that the Blacks are any good, but because the USA team would look like something approaching a Waffen SS recruitment poster if the actual, BEST players represented our country. Perhaps an aberrant Black or Hispanic here and there, but everywhere else, White, White, White, White...
The "politically-correct" public will acquiesce to an all-Black team in certain sports (in rare cases, such as hockey, which many consider a "niche" sport, few complain if it's basically a White-pride parade), but if a global sport with significant Third-World participation features an all-White, or nearly all-White squad, the fat ass, never-played-sports-in-their-lives club would flap their gay bingo-wings in a hissy fit of Broadway musical proportions.
So, that is why the USA team is destined to suck, because the best players do not actually play. Many are snubbed from the team in order to appease the feminists and ******* and disingenuous liberals who say "I love minorities" in one sentence and meanwhile the doorman in their Manhattan lofts knows who NOT to let in the building.
So, you have lame, useless American Black players who have no real right to be on the field, and will naturally be carved to ribbons by Teutons and Spaniards and Scandinavians and Mediterranean peoples.
In Europe, by contrast, while perhaps the best players do not always get to START, they are inevitably still on the squad and WILL play crucial minutes.
You could say the same thing about the NFL. Half of the black players in the NFL shouldn't be in the league, but they are because people assume they are good because they're black. So the quality of the play on the field is much lower than it would be if the best players, i.e. more whites, actually were playing.