Being a performer is the reason.
It starts in elementary school. The Christmas music comes out on September 1st! It continues all the way through December. By the time I've been singing it and playing it for four months every year for 34 years of my life, I'm over it!
I was just explaining to my show choir that I try to pick non-traditional songs for our slow songs, because I hate doing the same ones year after year! That's why I pick things like "Winter Song" by Sara Bareilles and Ingrid Michaelson and other newer titles that haven't been around forever!
I think I could go a year or two with out singing or hearing a Christmas song, and I would be perfectly ok with it!