At the beginning of the whole multiplayer thing (when it became somewhat popular), the top games would be played for multiple years and the developer would most of the time support the games for a long time. But that doesn't bring as much profit as releasing an update every 12 months for 60$ and then maybe you can even recycle old maps from the previous games and sell a pack for another 10+$.
At least CoD maintains this; there's still a good amount of people on BlOps and MW2. Now sports games? Correct me if I'm wrong, but don't they pretty much cut the servers for the old game? They also took out roster updates for the incoming year (when people would put out the upcoming year's rosters) from the download sections.
The advancements in sporting games haven't been enough to warrant a full new game; it's almost always graphic enhancement. They should restart the Madden and 2K series and just start from Madden 1 and NBA 2K I and update at a rate more similar to, say, Virtua Tennis so they're not required to "update" every year. This has led to rushed games anyway.