This is not always the case. In most of December last year, the market was red, and the rising market was only short-lived, so in general, last December was still a downhill market, we should not just see the green market and ignore the red market.
Mostly on December more down of price happens because people need money for holidays. Though the price is lower when people need it and no other source to get money, have no choice even the market is red which make the market more down. It is been hard to get green market during Christmas season and make you hold much stronger.