Too bad. I know how much you were looking forward to the ride.
From everything I've seen about this storm system, I think they made the right call. In the desert, the runoff rate in heavy rain is probably close to 100%. Add narrow, steep-walled, high-gradient canyons feeding the washes below, and you have a recipe for flash flood disaster. Also a potential for debris flows.
Of course, you're familiar with all that in the Santa Monica and Santa Ynez Mountains near the coast.