For the most impact, you'll vote with your wallet and let the Marriott property know that you wanted to stay with them but didn't because their reservations policies were too restrictive. I'm afraid that most hotels won't know they're losing business because of this issue unless people take the time to tell them.
That said, It's not the (potential) guest's job to act as an unpaid consultant to any hotel. I personally wouldn't contact any hotel about this issue unless I really wanted to stay there. I also might do it if I had a long history as a frequent guest of that property and therefore already knew some of the management team.