Understood. The loophole seems to be this: If I were grossly negligent and didn't cancel on time, and preferred to lose certificates instead of cash, I could just check-in on the mobile app, get my mobile key, and whether I actually ever physically arrived and when should be irrelevant to them. Feel free to correct me if you think I'm wrong. That's what was mentioned in Outrageous No-Show Fee Incurred At St. Regis Aspen, where OP said in the 1st post:

"Second, the mid-level manager suggested that if I run into this issue in the future that I simply check-in to the hotel via the Marriott app. This would likely work to avoid this nonsensical charge but I found this suggestion to be a cruel one since it was provided when arguing the charge and not when I called on Friday to kindly let the hotel know we would be late."