For most of Eaurope, and no doubt the rest of the world, football is a religion. You play it in the streets, you talk about it at work or when you're abroad on holiday and you watch it most nights of the week. It brings families together: when you get older and you stop having things in common with you're dad, you resort to talking about football and watching together. It's one of the most important things in a large number of peoples lives throughout the world.
Asking why Football never took off in America is like asking why Buddhism never took off in the states. It's too much of an institution to change with globalisation.