I think you're wrong about this actually, we're not there yet but football is definitely becoming a big deal here. When you read stories of the huge growth we've had what you have to remember is that we were starting from pretty much nothing football-wise. When I was growing up you played soccer as a young kid until you were big or coordinated enough to go play baseball or (american) football, there was a non existent domestic league, and no real way beyond some TV channels you didn't get to watch European football. It was a complete non-factor.
Now, our demographics are changing, immigrants from Latin and South America are the largest growing populations in the country, american football is going through an unprecedented concussion and TV ratings crisis, and NBC (one of our four major broadcast networks) has Premiere League rights where we can watch every single game and Fox is starting to show Bundesliga from next season I believe. Beyond that, you can go to pretty much any major city and find a bar showing games each weekend morning catering towards whichever team you support (including the City outpost here in New York, The Mad Hatter... let me know if anyone is ever in town and wants to catch a game) and just in normal conversation and whenever we go out, people talk about the Prem, which I promise was never the case before, ever. I can think or four or five places off the top of my head where I can get a City top within 30 minutes. Domestically even the MLS averaged 22k in attendance this year, which is pretty good for a league that no one had ever heard of or cared about five years ago. It's still a niche, but we're also a country of 330 million people, it still a little hard to find but definitely there.