The combination of geography, independence, and size are the main reasons that local sports grew to dominate the US sports scene.
When America came into its own after the civil war, most of the great soccer countries were several thousand miles away in an era when time and space actually meant something. Additionally, the US is big enough to have plenty of inter-state rivalries that basically serve the same purpose psychologically as an international rivalry serves between France and England (for example); i.e., you suck, we're better than you, and we'll prove it on the field. So being isolated from the major soccer powers probably led to just starting to do our own thing.
As for independence, well, we all know that the US in general likes to do its own thing and not feel like it's just "Europe West". So there is a level or contrariness there, I'm sure.
Essayist Chuck Klostermann believes that it is because Americans like to see dominance, which is more easily portrayed in a game like American football, where a score of 47-3 is completely possible. A 5-0 soccer victory is just as impressive, but it doesn't look as impressive on paper.
Soccer and Hockey are the same sport, basically, and hockey isn't that popular in most parts of the US either - but since we have a big neighbor that adores the sport, it bleeds into the north of the country. You'd think soccer would get a similar influence from Mexico, but until the last 50 years or so, the border between the USA and Mexico wasn't all that populous; Mexico speaks a different language than most Americans; and the center of power isn't in the southwest, so "American Culture" doesn't spring from that area. There has been a shift west and south over the last several decades, and not surprisingly, soccer also grows in popularity. I doubt it will ever compete with American football though.
So take your pick - soccer's homeland was across an ocean; the USA doesn't have a lot of nations on its borders; we like big scores which show if there was a severe ass kicking; and so on.
That said, seeing that English goalkeeper bobble the ball away was quite delicious. :D