"Start with the observation that, unlike a car or a laptop or a share in Coca-Cola, every house is a little different. Any particular house may match a family's needs awkwardly or perfectly. Finding out just how well a given house suits you is also a costly and time-consuming business.
That means that buyers like to house-hunt in 'thick' markets, when lots of houses are for sale, and a very good fit is likely to come up quickly. It is no fun to house-hunt in a 'thin' market, where the meager crop of houses is unlikely to offer up the dream home.
If [researchers] are right, then the housing-market dynamic is something like this: Buyers slightly prefer to purchase houses in the summer, so house prices are slightly higher in the summer, so sellers prefer to put their houses on the market in the summer-and with more houses on the market, the market is thicker. That means that buyers are more likely to find the exact house they want and so are willing to pay more. With prices higher, more sellers are attracted into the summer market, and fewer will contemplate selling in the winter. And so on. The self-reinforcing process can produce a large gap between summer and winter prices."