I love this season. My absolute favorite. Advent and Christmas, cooler weather (finally get to turn off the air conditioning) and so forth.
For many of the same reasons Kazimierz mentioned -- O Antiphons, Advent/Christmas songs, Matins for Christmas Eve, etc.
And December is chock full of feast days. Those are the "Holidays" for a Catholic.
St. Nicholas Day
Immaculate Conception
Our Lady of Guadalupe
Gaudete Sunday
And that's just the first half of the month.
And let's face it: most families have 1 or more birthdays in November and December too, for whatever reason (maybe it has to do with the beauty of Spring 9 months earlier?)
Let's just say December is the birth-month for MORE than 1/12th of the population, which statistically shouldn't be the case. November too.

We have had the furnace running for three weeks here already. Temps in the 20F and colder we had, now getting close to freezing again, which is a pain as the snow we have will melt a bit then things freeze overnight. Awaiting patiently - trying to anyway - for the next surge of Arctic air from Siberia and a good helping of snow sometime early in Advent. The "joys" of living at 53 N Latitude.

It was a lot more fun as a kid playing in the snow and cold though. Traditionally, there was always some snow on the ground for the start of Advent (the 70s were above average for snow and low temps, thus a cold-ish VERY white Christmas is what I grew up with.)
Apparently it will be a brutally cold and snowy winter this season a few sources say. And so I keep praying!
I would have a terribly difficult time (and have had) when I did not have sufficient snow and cold for Advent and the Yuletide. It is built in, spiritually and psychologically.
Benedicite glacies et nives!