The Yankees signed Colon off the scrap heap last season and they ended up getting a very strong performance out of him for the first half of the season. Midway through though he pulled his groin and never got the same movement, velocity, or control of his pitches again.
It might not have been the injury though, he might have just broken down after piling on a ton of innings during the previous winter and then early in the season. Something he has not been used to as he hadn’t pitched that much since 2005.
Either way, the Yankees currently have seven potential starters for five spots so Colon was not needed.