Could it possibly have something to do with the other members of his draft class all seeming to get extensions recently? Did they not want to risk DD being disgruntled by the fact that Lawson, Curry, etc. are all being extended and he was not?
The cynic in me says "who cares? he's not good enough to worry about that sorta thinking". Plus, BC could have made an unofficial verbal commitment to his agent, asking him to wait until the offseason to make it official, to give the Raptors as many options and as much financial flexibility next offseason as possible (ie: DeRozan's $4.5M cap hold VS his $9.5M salary = $5M less cap space to work with). That appraoch would give BC more options to build the best possible team, with the intention of DeRozan being a key part of that team. I just don't get the timing or the amount, for a guy who I don't think is worth more than $6-7M per season at this point in his career. That's a lot of money and a lot of lost opportunities, based on potential.