Actually, it's not that easy. I noticed once that one of the hotels where I'm a repeat guest was listed incorrectly on Google Maps. The Front Desk Manager was checking me in so I mentioned that. She groaned and proceeded to tell me how they've been trying for months to get that fixed. They would submit a request and it would get changed only to be changed back whenever some behind-the-scene technical process was run.

On a more general note, it's also possible the hotel and/or Marriott doesn't know the map is wrong. It's unlikely that anyone from the hotel ever looks at Google Maps. (They already know where the hotel is located.) Unless someone reports the problem to them, they can't fix it because they don't know it's wrong.

Although it's not your responsibility, perhaps you could take 3-4 minutes to notify Marriott of the error via the website. You might be helping future guests find the hotel.