In truth, everyone played some type of a role..
EA approached the NFL about an exclusive license and then after aquiring it locked up all meaningful football league licenses and ESPN for good measure.
The NFL's business model involves exclusives with most of their product line and are also overly agressive with unauthorized licensed uses like youtube videos and small time mom/pop shop t-shirt sales. It was probably only a matter of time before the NFL chose to do a more lucrative exclusive video game deal.
2k hurt themselves with that $20 pricetag that got EA to drop it's price to $29.99. Lowering the prices of all the games damaged the value of the NFL license and the NFL was not pleased with that decision.
Football fans even played a role, imo. In the years leading up to the deal signing fans became more attached to certain products and were less willing to try other games. Titles like NFL Fever and QB Club failed in an open market because of this. With fans rejecting several of the choices it made it an easier decision for the NFL to opt for a single developer contract. The only backlash was from 2k fans since other titles went under on their own and Madden fans continued to enjoy thir game.
Regarding the deal ending, I'll just say the same thing I said in another thread. I believe it
will end because EA
doesn't need it and the NFL won't find other takers. 2k is in dire straits, they can't outbid EA for an exclusive. They can't spend money developing a generic football game that will be lucky to sell a couple of hundred thousand copies and there is no point developing an NFL game when there isn't a possibilty to release it for another 2 years anyways. Not to mention that game would only be possible with an open license so it most definitely will have a Madden 14/15 (whichever) to compete against. 2k has about as the same odds as those fine soldiers at the Alamo did, imo.