My thinking is they were going to greatly reduce his playing time and/or possibly deactivate him with other players returning and because of his past injuries, he could have possibly said he was injured as the reason for the demotion which would have locked them into to next year's salary.
I am not saying he would have done that, but rather they likely went proactive just on the off chance he (or his agent) took that route when his playing time was reduced or he was deactivated for a game.
This combined with likely already knowing they were not going to bring him back next year made the decision to address it now more feasible and relevant.
Again, this is just my thoughts.