I watched a game of American football once and was blown away by how many adverts there were. It's such a slow game too - so much stopping between tackles for deliberation (seemingly). Don't get it personally.
I was going to go with money -- the amount of money to put kids through soccer in a competitive program in USA/CANADA is way more than the competitive programs in europe. That immediately drops down the amount of talent that can make it through the system + anyone who is particularly good and has any connections to europe goes there to level up faster by playing more competitive players.