What if the GM said, "sorry, no refund?" The point is that Marriott is trying to claim "peace of mind" with bookings, including nonrefundable ones. To me, that comes with certainty that I can cancel at any time (or as least as specified on the policy), not "'let's see if the GM would be generous enough to let me off the hook."
LAX
I'd bite the cost and kick myself for being stupid in the first place for making a non refundable reservation.