In a post about a few things, Doc Searls asks this about soccer's (lack of) popularity in the US:

Is the relative lack of professional soccer popularity in the U.S. perhaps due to the absence of advertising opportunities, since the game goes on for 45 minute periods with no time outs?

That explains part of the TV coverage problem (although banner ads would certainly work). Part of it is simply what Americans are used to seeing. When we watch a sport on TV, we are really, really used to instant replays. With the way a soccer game flows, there's often no time for that. Sure, using a DVR you can do it yourself - but it's not the same thing.

Another thing is scoring. Soccer games can go a long, long time without a score - the just finished world cup finale went from minute 19 to the shootout without any scoring - and after the Zidane headbutt, Italy had a man advantage for about 10 minutes. American sports fans are simply used to higher scoring games.

I think it's as simple as "tastes differ". Trying to "fix" soccer so that Americans would like it better would probably irritate the (very large) fan base in the rest of the world.