The way I see it is Christmas time is in the middle of winter. In the oldern days it was common not to know anyone that lived above the age of 50 so winter time would claim many people's lives. To cheer themselves up, people would gather together to throw parties. They were facing a dangerous time when lots of diseases were spreading through the air because it is colder and darker so the viruses can live for longer. People would get flu, Tuberculosis, small pox and even measeals but these days most of the diseases have been eradicated. That sense of danger and death is still there but we ignore it.
This is true of every culture, the Jews celebrate Hunnokka, Christians celebrate a belated birthday party for their saviour. The pagans would pay tribute to the god of Fertility; my point is everyone throws a party in the middle of winter to cheer themselves up.
I call it universal Festivities. Dealing with the winter.