American soccer is a very young sport. In comparison to other countries in which the game has been played for hundreds of years at a very competitive level, in America, soccer has not quite taken hold.
Whereas basketball and football and baseball dominated the sporting landscape over the past century, soccer never quite gained the same foothold that it has in other areas of the world. It is the number one sport in most of Europe, South America and Africa. Brazil is married to it, England is now the central domestic league in the world, but it was Spain before them and Italy before them.