Why did the yankees release Chan Ho Park?

Something's confusing me. He had an magnificent ERA, a marvelous number of strikeouts, and very few walks or hits given up, as well as very little saves blown. Although he gave up a couple runs last year, he was one who could send the ball blazing over the plate snapping into the catcher's glove, like the ball was a rocket. He was great to have on our team, why did cashman release him?