They can, and have... my opinion:
Soccer has certainly grown in popularity in the USA. Almost all kids in the USA are exposed to the game now. Around me, and some other areas I have some knowledge of, soccer is usually the 'first' team sport American kids are exposed to. Never the less:
It's not in our genetic makeup yet, at least as compared to the rest of the world.
Here, (again, around me... can't speak for the mid-west or the east or even the LA and SF areas), as soon as possible most of the more athletic kids move into other sports. And 'as soon as possible' comes around pretty quickly.
The game 'not being in our genetic makeup' just proves, ( to me, anyway ), the excellence of what it takes to be a WC team.