JK was saying it was an "ego" thing. Marcus has felt like he has been a good soldier watching Rondo, Nelson, IT, Kyrie, Kemba play PG ahead of him. Maybe he (or his agent) see the writing on the wall. DS is a better offensive PGGiven that the Celtics just signed Smart to a lucrative extension, and Schroder is here on a 1-and-done deal, I'm highly skeptical of Karalis' speculation.
Also, the money/contract is irrelevant, from Marcus' perspective, since he felt and has stated that he signed for a discount for the second time. MS certainly doesn't see it as a "lucrative extension".
He probably sees it as a tradeable contract