As to why, this is pretty obvious. November and December is cold in most parts of the country and it's also the holiday season. The last thing somebody wants to do or think about doing is moving. He said absolutely the best time for rental activity was in the summer. From my experience he's absolutely right.
I can't say this is true for every part of the United States or the world, but definitely in Florida. Do some research and find out when the best time for your market is. Don't be afraid to take a short term 7 month lease so that you end up renting it out again during the hot months.