Christmas is also an invention of marketers, at least as we celebrate it today. Depending upon which Christian country you are from, or your ancestors were from, and whether you/they are celebrants of Eastern Rite, Roman Catholic, or Protestant (not to mention which calendar is used), the date of the winter celebration we in the US and parts of Western Europe refer to as "Christmas" can differ from today (Happy St. Nicholas' Day!) to the end of the Feast of Epiphany on January 6th.

So you see, not even all Christians celebrate the birth of Christ on December 25th. The idea that this is a universal Christian holiday is totally erroneous, and a belief usually held by poorly educated Americans, who have a tendency not to see beyond their own noses.