There are ups and downs in any marketplace. In the LEGO secondary market, prices on the whole, usually rise in the Fall and early Winter and drop after the New Year.
My theory on why some large and expensive exclusives drop when they should be rising is based on the new wave of resellers. This is a newer phenomena. Year ago, almost all LEGO sets would rise though the Holiday season, but I believe now the current makeup of resellers is to flip for quick profits, instead of holding for long term gain. Many new resellers get anxious holding a set past a year, so they sell these big sets that they made some quick money on to lock up profits. Over time, after more exclusives are resold, the prices continue to increase at a solid pace.
If people would just look at the history of some of the current $1000 sets out there, you would see it was a slow climb for the most part, over yearS, not months. People selling their Town Halls right now is understandable, but my sets increase in value long term with each early sale so I really won't complain.