In the temperate latitudes it tends to get dark and gloomy in the fall and winter. Many people get depressed during that time to a greater or lesser degree. This may or may not be directly related to the historically very real possibility that winter might mean freezing to death or starving. People living in those areas created a number of festive holidays to compensate.
Thanksgiving-type: Yay! The harvest is in! We probably won't all starve to death during the winter!
Solstice-type: Yay! We're technically halfway through the winter! We probably won't all starve!
New Years-type: We're reached a turning point! Things won't keep getting worse, the world has been reborn and we're on our way to spring! and/or Spring is already here! Some cultures do it later when it's more clear that spring is actually here and some do it earlier when we more clearly need the cheering up, but a lot of them are clustered around January and February. (And of course some don't do it in the winter or early spring at all, but those seem to be a comparative minority.)
This presumably worked quite well when we were mainly agricultural civilizations.
Now however life has gotten a lot more complicated. Most people have jobs that are entirely unrelated to agriculture and which continue on throughout the year without a huge amount of variation in what they're doing on a month-to-month basis.
But even with a constant year-round workload you need to review everyone's progress from time to time. You need to see if people have met quotas, have accomplished goals, and if they ought to get a raise or bonus. And what better time to do that than the already previously established end of the calendar year? It just makes sense to review your progress over the past year right before the end of the year, right?
So starting about a month or two before the end of the year most companies ask employees to judge each other, and more importantly themselves. Which just happens to be during a period of time when, statistically speaking, everyone is most likely to be gloomy or outright depressed to begin with. Feeling depressed leads to poor self-assessments. Poor assessments lead to feeling depressed. And of course poor assessments can lead to lack of bonuses or even lack of a job (or at least fear of such) during a time when you're supposed to be spending money on presents and decorations and travel. And everyone is supposed to be happy during the holidays! WHY AREN'T YOU BEING HAPPY? IF YOU DON'T CHEER UP AND GET A GOOD PERFORMANCE REVIEW YOU'RE GOING TO RUIN THE HOLIDAYS!
And all because we wanted to cheer everyone up in the first place by stressing that this is (around) the time when the world is symbolically reborn.