why do they say xmas instead of christmas

Oh, that's a good question. The reason people use the term "Xmas" instead of "Christmas" is because it's a shortened form of the word "Christmas." The letter "X" in "Xmas" represents the Greek letter "chi," which is the first letter in the Greek word "Christos," which means "Christ." So, "Xmas" is just a way of shortening the word "Christmas" while still retaining the reference to the birth of Christ.