Jared Sullinger is one of multiple players in a contract year with the Boston Celtics. After they failed to reach a contract extention it became clear that this was a prove it year for Sullinger. The young big man had his sights set on a max contract but he needed to prove that worth to the Celtics. While Sullinger has been improved and is a crucial player to the Celtics this season, he still has not shown that he should receive a max contract.
It is not only an issue of the Celtics being reluctant to pay Sullinger that kind of money.