The holes they don't use are either 1) too weak, 2) not interesting ... i.e. everyone would layup on 4 of Clyde, 3) too quirky for championship golf - 9 of Clyde and 1 of Squirrel or 4) not in the right spot.
I haven't played the course in a long time, but I do wonder about the tee shot on 13. I feel like the severity of the turn makes it work better for a 380 yard par 4 (1 on Primrose) versus 450 yards (1 and 2 on Primrose).