why do people write xmas

The use of the "x" in "xmas" is actually a shorthand way of writing "Christ" without having to write the full word. The "x" is meant to represent the Greek letter chi, which is the first letter of the Greek word for Christ, "Christos." The use of "xmas" is believed to have originated in the early 16th century, and it has been used ever since as a more compact way of writing the word "Christmas."