He's too important to their image and their selling point as a destination for elite free agents. If a guy like that decides to leave money on the table cause he wants to be here, presumably because he's a childhood Rangers fan, but even in an alternate scenario just because he likes NYC or because he likes the organization or exposure....
... you can't deal him after a year. It's a betrayal. If he wanted to be somewhere else, he could have held out for top dollar.
You disrespect a free agent signing like that who specifically wanted to be in NY, and agents and GMs will remind future free agents of that fact.
It's different maybe a couple more years down the line. Maybe in his contract year. But not this year, no way.