The over weight condition of people in America is sometimes referred to as an epidemic. It might explain why soccer has not gained a significant foothold. In other countries soccer is played from a very early age through young adulthood. This appreciation helps fuel its popularity.
It also has very few real requirements for the game, a ball and space. There are sometimes ingenious methods used to create a ball.
Americans are a relatively physically inactive people. Therefore they will not gravitate to a sport such as soccer that requires a great deal of physical exertion. More sedentary pursuits captivate them, such as video games.