The problem is not with Perk not accepting the offer. In all, it's a low offer to him and I don't know why it should be expected of him to choose to do so. No one would have.
The problem lies in his apparent intention in playing the market, coupled with the amount of money a player of his stature deserves would have been to rich for us, particularly if he's looking for a long contract.
We can easily and happily overpay him to keep him here for a short amount of years, 2 years say, but big long contract for him would be a mistake so it was either Perk accepting a low offer to stay with us, which shouldn't be expected of him, or letting him go for nothing. So we traded him.
So in all, the Celtics found themselves in a no-win situation with a player who's currently injured and coming off a big injury. And Perk, well he clearly didn't give assurances to the team of his willingness to stay for a responsible/just contract.
We talk about loyalty, but loyalty goes both ways and teams have little protection against players leaving teams with getting no value. And remember, our cap situation severely restricts what we can do in the offseason.