There are many possible factors. One of them is that many celebrities are addicted to drugs or alcohol. And during this time of year, people often ingest much more alcohol than the rest of the year. There is also highly increased depression from lack of natural sun light from the sun going up later and going down sooner. There is also highly increased loneliness during holidays where families are supposed to be together, for people who are alone and have no family.
All of these reasons make people less likely to want to keep trying to live in this time of the year. For people who are having a lot of health problems like sick and elderly people, the reason they live so long is because they are working so hard to try to live. So if they mentally and spiritually stop trying, this usually makes the health problems get much worse. This is also related to how often very old people will stay alive to see something important happen like watch 2 people get married or watch a baby be born, and then will die soon after that event happened. Because they were staying here waiting specifically to see that event, and now they are ready to go.