I can explain why, even though I am an atheist: People miss Christmas. They miss having a holiday that was pretty much universally celebrated (of course it was never "universally" celebrated, but it felt that way.)  They fear the need to avoid treading on people's sensitive toes by saying something that might... set the other person off. They mourn the loss of Christmas and it's replacement with the generic Holiday.

I feel the burden is on the other half: instead of trying to not to offend, we should try not to be offended.

Merry Xmas!