I think it is the fact you have a wider audience from the start, so more people to ask their parents to play. Also hockey needs hockey sticks, which break etc. But yeah, i agree with your point that football is not a cheap sport either. I also think another clue to the socioeconomic backgrounds are the number of black athletes. Black families are generally worse off than white families and hockey has very few black players, whereas football has a lot (although the QB is often white, which is odd)