Springs, who signed a three-year deal worth roughly $10 million in 2009, and head coach Bill Belichick didn’t seem to share the same beliefs when it came to football, and that’s never really the best thing for anyone involved. Springs believed he was best suited to play man coverage, but Belichick's defense requires a heavy dose of zone coverages from its cornerbacks. That clash probably had a lot to do with Springs' lack of playing time.
Springs also suffered a knee injury at some point last summer, and it showed up on the Patriots' injury report throughout every week of the season, yet Springs often denied that his knee was bothering him. He was inactive in four consecutive games from Weeks 10-13, but he had full participation in practice during every session in that time span. So, for whatever reason, Springs was really a healthy scratch during each of those four games.
Springs turned 35 in March, and he is obviously on the downturn of his career. However, he did seem to play well most of the time he was on the field last season, so he could have been a serviceable member of the team in 2010. The Patriots have a good core of young cornerbacks, led by Leigh Bodden, and they're driven to develop Darius Butler, Jonathan Wilhite, rookie Devin McCourty, Terrence Wheatley and possibly special teams ace Kyle Arrington.
Springs' presence would have only hindered that youth movement, especially if he wasn’t always the most straight-and-narrow locker room citizen (it sounded like Springs vocally backed linebacker Adalius Thomas during his spat with Belichick). And Springs had no impact on special teams, which is essential for someone who is in a gridlock for a roster spot.
It basically comes down to this: Springs was serviceable on the defensive side of the ball, but something strange was happening behind the scenes. For a 35-year-old with a decently-priced contract, it's not the least bit surprising he was asked to pack his bags.