Lol it's so deeply ingrained right in front of everyone's nose. Magic Santa, magic reindeer, magic elves and that's just the stuff before propaganda like Rudolph and Frosty came around.
God forbid I get a Harry Potter book on Christmas and being magical thinking into this mess.
The first references we have to Christmas trees are in 16th century Germany. They probably didn't come directly from any pagan traditions seeing as Germany had been Christian for multiple centuries at that point.
I’ll do you one better: Why is Easter a fertility celebration? None of the accounts of Jesus’ resurrection directly tie it to fertility. These became popular as Christians became exposed to cultures that had spring fertility festivals.
The religious celebration of Christmas includes Advent wreaths, church services, and traditionalist music (Joy to the World, Silent Night, etc.) Everything else is the secular celebration.