People are used to saying Merry Christmas, which means to pray for blessings. Christmas is sacred to the west and is the birthday of Jesus Christ. It can be said that Merry Christmas has become their consensus.
There is nothing wrong with the meaning and usage of Merry Christmas, but they have formed a fixed collocation of "Merry Christmas" in hundreds of years of history. Santa Claus is a Santa Claus who quietly gives presents to children on Christmas Eve. It can also be called Santa Claus or Santa Claus.
Merry in English
Merry has always had a pleasant meaning in English, but a Christmas Carol by Dickens 1843 gives merry the meaning of "slightly drunk".
For example, there is a famous saying in English: Eat, drink and be merry, because tomorrow we will die. This sentence means "Eat, drink and be merry, and we will all die tomorrow", but in fact it means "Life is short, eat, be merry".