I like the example that J. Rose is demonstrating. He's being an example of self-LESS-ness (Big contract, big ego w/offensive skill sacrificed for the team.). Despite what people may think Jalen can still score; ask anyone in that locker room. However every good team needs a "sacrificial veteran". Someone who does not get a lot of playing time, fills in where ever they can and is an anchor and inspiration to the young guns (A role that they never allowed Patrick Ewing to fill which would have ushered in the new era sooner). We don't want Steph or Francis to play that role; we still need them on the floor. Jalen will have a greater team impact in practice and the locker room.
Since we have to pay him for the year anyway, let him be the locker room leader (a rather expensive one I might add, but the milk has been spilled). He's a great fit for the team because he is injury insurance for the 1,2 & 3 spots. Finally, if he continues to accept his role he can emerge as an x-factor later on in the season when overall league defense becomes quite stingy. In those cirucumstances there arises situations when you can only rely on the confidence and experience of your veterans to get the edge (i.e. Steve Kerr on the '03-04 Spurs Championship team).
Besides, Jalen knows that this will most likely be his last year as a player it is a tough pill for him to swallow i'm sure. He's most likely looking to bow-out gracefully.