Because awful lot of it “just so happens” to look exactly like festivals and traditions from before the supposed birth of Christ or before Christians arrived in an area so much so that Jehovah’s witnesses and the Puritans won’t celebrate it, seeing it as a pagan holiday.
Sure, you might throw an angel or star on top of a “Christmas” tree but the bringing evergreens is a pagan thing, an act of sympathetic Christmas 2021 Australia magic that reminds people the green will come back. Giving gifts? That’s a very recent thing, as gift-giving was traditionally done on the New Year, and we know Santa isn’t Christian.
Ultimately, the only truly Christian part of Christmas is the nativity story and the actual mass for Christ. Since strictly atheist (or other religious) families don’t go to church at all, it’s pretty much exclusively Christians doing that bit.
The rest of us are doing what humans have been doing in the midwinter for thousands of years, spending time with the family sheltering from the dark and cold, and having a feast.
If you take elements of Yule, Saturnalia, and Modraniht, throw in a dash of European druidism, and force it through a filter of Charles Dickens’s Victorian England, you get what we currently understand as Christmas.
It’s theorised that theme of death and rebirth are so prevalent in these pre-Christmas festivals that it’s possible that the “Christmas” wreaths and trees are in fact representations of female and male genitalia– something to think about when you polish those Christmas baubles.
to exchange gifts, to enjoy some good food and drink, to decorate the streets and our homes, to listen to the great music that religion has inspired, to watch some soppy movies on TV to meet family and friends that we rarely see … and because we were celebrating in mid-winter long before Christianity took over Europe.
In the Northern hemisphere Christmas took over the pre-existing mid-winter festivals such as Yuletide and changed their meaning. Christmas 2021 Public Holidays Why do you think we have Yule logs and Christmas trees? They are nothing to do with Christ and everything to do with the much older mid-winter events.
In the same way Christianity seized on the pre-existing Spring festival of Easter … a celebration of life returning after winter, with the egg as its symbol, because they saw that it could be connected to the idea of the resurrection of Jesus.