We have more options, that's what I think the major reason is why soccer will never approach its worldwide popularity here.
I agree that Americans might not watch US soccer as much, because we aren't the best at it, but I don't think America is alone in that. Other countries have access to other sports, but watch soccer. Why? it's what they grew up with, what they are passionate about, and the one sport they can compete on a worldwide level.
Not too dissimilar from America, except we dominate multiple sports.
It's a weird thing to me, the continued discussion of soccer, and why hasn't it approached global popularity?? The annoying part is that sentiment, underlying everything, that Americans are somehow lagging, missing out, don't get it, are too boorish, or not sophisticated enough to get the subtle beauty of blah blah blah blah........ The US fan isn't lacking because soccer isn't as popular here, we are just a different country. Do Canadiens wring their hands over why soccer hasn't approached hockey? I doubt it.
Hey, give a bunch of Brazilian kids a hundred years ago some basketballs, turn the best soccer player of all time into a shooting guard, and history would be different.
For a LOT of countries, the only homemade superstars they can see on a regular basis are in soccer. So soccer is the sport they care about.
The US is different. We have LOTS of homegrown stars, playing several sports at the highest level in the world. Between baseball, hockey, football, NASCAR, it's pretty tough for a sport to horn its way into the forefront. Frankly, I think soccer is doing pretty well, all things considered.