Exposure, habit, heritage. They are "big" sports too, for big people. But both were somewhat invented in America though similar games were played centuries ago. Million dollar contracts are to generate even more millions for the owners. Whatever the market will bear is the rule of economics.
But as in most arena sports, people play them as children and if people can't do anymore - people watch - the world over.
I am not a spectator. I am still participating in cycling after a youth with the rest- football, basketball, baseball, soccer, etc.