They didn't think they needed to because Parker was supposed to fill that role. And if the coaching staff didn't think they needed more perimeter scoring, why do you think they signed Kevin Martin?
Also, last season was last season. The Warriors are actually much better this season, as scary as that sounds. This Warriors team easily sweeps last season's Cleveland or Memphis teams. There's nothing wrong with the way the offense is "structured," what's wrong right now is on the player side of the equation. Zero consistency from the role players.
This series is also a poor barometer, since Memphis is gutted. We'll see how they measure up against the Thunder, but I'll predict right now that if Patty, Tony, and Danny continue to play like they have, we're not advancing. Kawhi and LMA plus Whack-A-Mole just isn't enough. Also worth mentioning is that Kawhi is going to have to carry a big load defensively in that series. We can't expect him to score 25-30 every game while also playing world class defense on Durant. He needs perimeter scoring help. That's another reason I've been so adamant about another perimeter player being a threat. Takes a huge load off Kawhi.