Mark, track and field has the highest participation levels on any sport in high school and the amount of people who run dwarfs any other sport. It is not for a lack of understanding of the sport why it isn't popular.
And this is why the problem is simply- marketing. All of those 10k joggers and high school kids should be watching the sport.
Intersting- I asked one of my classes (15 yr olds) how many watched the Super Bowl- everyone raised their hand (23 students). I asked how many watched it for the actual game. 10 raised theur hands and the other 13 talked about how boring football is. But they watched- marketing.