I think you nailed it with your last sentence. The majority of people are "NFL" fans, not fans of the game of football. Which will translate into poor sales and that is all EA, 2K, MS, Sony, etc care about. I am not a soccer fan, but I think soccer fans love the game of soccer more than the players and/or teams and that is why non licensed soccer games do well.
I would love a fully customizable football game. I remember about 5 years or so ago (not sure if they still have it) in the Madden PC game, you could create your own teams (logos, jersey, helmet, etc) and your own league. I had a blast with that game. Many gamers on the web used this as an opportunity to create old school unis and NCAA uni's, but I created totally new teams.
Unfortunately, I think I am in the minority and I am afraid that is 2K's thinking as well. Let's hope it is just taking much longer than expected to make this a fully customizable game and they don't want to commit to anything yet.