Holidays are based around family, friends, and most importantly couples. We are marketed to by various companies to exchange gifts with our mates, take romantic getaway vacations, and on top of that Hollywood releases several romantic comedies tied into the Christmas and New Year's Eve Holidays. A lot of romantics want to stay in relationship at least through Valentine's Day.
Having said that there are other people who "schedule" their breakups before the holidays! They don't want to have to go through the motions with someone they have already decided is not a good fit for them.