I think people are actually selling more than buying at this time of year, at least those who celebrate Christmas and New Year. Most will actually spend some BTC (by selling for fiat/or directly) to buy gifts, food and drink, decorations and all that is being bought this time of year.

People actually buy BTC long before so they can sell it and make a profit in this period, and this was a good strategy this year as well, at least for those who bought in the first few months of this year, they doubled their money.