I still fail to comprehend why people celebrate that the Eath has made X rotations and then at a new cyclus (say a year) they all of a sudden whish the best to

I still fail to comprehend why people celebrate that the Eath has made X rotations and then at a new cyclus (say a year) they all of a sudden whish the best to other people, make plans for the new cyclus and even stay awake deep into the night to celebrate it.