Not a big surprise, but I'm not sure it's to any major extent. In '02, if I recall, Univision had a significant ratings advantage also.
Much of the problem is cultural in nature. The European stereotype of Americans as garrulous, overly friendly near-rubes is, to some degree, based on fact. Our sports commentators have this tendency to chat away, spouting facts and rumors, and often making the coverage more about them than about the game. I can remember the early years of Phil Schoen doing MLS, when he ran an online bulletin board asking for viewer comments. They were, almost uniformly, "shut up." Other viewers asked him to carefully listen to the Premier presenters and try to emulate them. In the end, Phil pulled back on chattiness, and became a bit more reserved, and he's considerably less irritating to listen to now.
There's also a lack of awareness on the part of most American announcers of the theatricality of the game. If you listen to English coverage, or to Univision, you'll hear a clipped, tense, style. Primarily it's focused on who has the ball, and what the last official's call was. The result is that you build the tension in the audience that's released when there's a goal. If one views a game with ex-pats in a pub, one will notice that it's almost like a religious service. There's an intense focus on the game, not a lot of happy talk and chattiness, then an explosion of sentiment when a goal is scored. That whole atmosphere is lost if there's a running free-form commentary.
So, to me, the whole issue is 'less chat, more focus'. If they could get that right, you could almost forgive the limited knowledge.
When it comes to commentary for soccer, less = more is a good rule to follow.