Soccer is half a sport; it requires use of only half of the body. Think about the most exciting plays you see in soccer. These typically involve a diving save or an aerial kick. These types of movements involve the full body, and therefore are more compelling to watch.
Football, on the other hand, requires use of the entire body. There is nothing like the rush of running into another person at full speed. This is an experience that others shun for fear alone. This is the problem. Soccer is a much safer sport. Indeed, its players often feign injury, but less often are actually seriously injured. This melodramatic acting and whining, btw, is pathetic. In football, a player is motivated not to show pain or injury. This speaks to the more honorable side of man.
I have taken the approach in comparing soccer to football, which doesn't exactly cover the general theme of your question. I hope, however, to have highlighted some reasons why soccer is simply an insufficient practice for many Americans.
