How, if the US was built by immigrants from the countries that LOVE these sports? There always has been a strong audience. But, the audience that loves it are the "people" no one really cares about - foreigners. Watch spanish TV, it's all soccer.
More so, are you ignoring the millions of hispanics and people from europe, africa, australia, middle east, asian, etc., who currently live here and love the sport? Maybe they're not as seen as some obnoxious football fan, but they're there.
But now we're getting into why people don't follow the game, which is different to why TV networks don't promote it. TV network's specific reason is commercials, on regular, everyday games. An exception or two can be made, but overall, unless the way the game is played gets changed, normal coverage of a soccer game would suck for advertisers.
I am not arguing the relative worth of each sport, nor the relative worth of that sports' fans. I am just looking at the facts. There are 100,000 fans at every University of Michigan home game. People pay hundreds of dollars to see 1 of 80 New York Yankees home games, and those are the cheap seats. The Super Bowl is the biggest TV draw for the entire year. These are the facts. Advertisers follow the crowd.
At the same time, I wouldn't be surprised at all if soccer became the number 3 sport in the US within 20 years, perhaps even surpassing baseball at the high school and college level. We could be seeing prime time soccer on one of the major networks within maybe 15 years. Soccer is quickly becoming more popular in the States, and I see nothing wrong with that whatsoever. The more sports to pull fat kids off the couch the better off we all will be, IMHO.