Despite the fact that some people feel that it is an attempt to remove "Christ" from Christmas, it's actually not. In Greek the letter "X" is short for "Chi", rather than being short for "ex". It has been used, possibly as far back as the first century - by the Church itself, as an abbreviation for Christ (then later Christmas, and even the word Christian/Christianity).
I don't know but I hate it when people write it like that. They're putting an "X" instead of Christ in Christmas. It's called Christmas. Please show some respect for the holiday and not put an "X" in it!
In Greek, the original language of the New Testament, the word for "Christ" is xplotoc, which begins with the Greek letter that is essentially the same letter as the English letter X. So, originally, Xmas was simply an abbreviation of Christmas. No grand conspiracy to take Christ out of Christmas. Just an abbreviation.
I believe that it's because they want to take Christ out of Christmas. Mas means to worship or to give praise. Therefore Christmas is the worship of Christ and people are trying to take the religious asset out of it