I don't think this is true, and a large portion of the US is heavily invested in the World Cup while the US is in it, and that portion only grows the deeper the team gets. It just hasn't been there for about 20 years since the US hasn't gotten past the round of 16. Hell, for the round of 16 game this cycle, we were at a bowling alley, and every TV had the Netherlands-US game on, and there were over 100 people there watching it. It will also be in the summer when there are fewer competing sports.