This is the same reason why you would never see Coca-Cola and Pepsico products in the same game. Why would you want to promote your opponent even with everything else being the same? I'm sure EA wants to use the ESPN license, but the NFL is telling them not to because they want to promote the NFL Network.
It may not make sense to you, but the NFL is using good business practice here in order to put a minimal showing of ESPN in their product. They don't want you going to ESPN, ESPN2, or ESPN.com for any NFL information. Using ESPN products in the game encourages that, and thus the NFL will say no to it.