Answer:
Something that our ancestors did in the past, and we still do is celebrating new year holidays in December.
Even in multicultural countries like the U.S. or Canada, where not every population group celebrates holidays in December, the majority of people still do, as they did in the past.
The term that can be suggested for this phenomenon is "tradition", which can be defined as the set of beliefs, customs, rituals, and behaviors, that are passed down from generation to generation.