We have been in Marmaris about 15 times, always end of May, August and end of September. This year we have been in February and we sincerely think that there should be some action taken to promote Marmaris in the "wintertime" It was very difficult to get a flight at first because it is not possible to fly directly to Marmaris. First flights only start at the middle of April, anyway we took the risk and booked via Istanbul to Dalaman on the way up and back over Bodrum on the way back. We had a fantastic time, of course the boulevard was empty and all bars and resturants closed but in the old centrum and the harbour there was enough to do. We sat outside most of the day and the weather was very nice, all people came out of their houses enjoying the first sunshine, we could not have imagined that there was so much life in wintertime. Disco's where packed Friday and Saturday. Of course there where hardly any tourist but all the nicer it was.
I hope that this information might help but maybe it is never the intention to get tourist in Marmaris in the wintertime to give the people a rest but it might help to earn some extra money because most of them did not have any money left 
All the best