Sacred Haven of Debauchery

When your own depressing existence, oozing from every pore, prevents you from participating in the festivities even once a year, that's bad. And yet, this isn't just an "ordinary day" that can be replaced with any other by gathering together. It's a new, major chronological period when people celebrate another orbit of the Earth around the Sun; it's a holiday of astronomical proportions. You don't need to go to math class at school or have anal sex in the office; the pre-New Year suite, the feeling that the whole planet is celebrating with you, unlike some individual birthdays, the pleasant contrast of colorful tinsel and string lights on a green Christmas tree, snowflakes lazily falling from the sky, and Santa Claus, a pedophile, shouting "ho-ho-ho." All of this happens only once a year. A year is a long time.
These are all the reasons you were interested in. Whether you want to be happy about it or not is up to you.