The X in words like X-mas and more rarely, Xtion are not getting rid of the word “Christ”. In fact, the “X” sign used there isn’t really the letter X! The X sign is actually supposed to be the letter chi in the Greek alphabet. The Greek spelling for Christ was Χριστός. The use of the X in that way dates back to the 16th century. Some uses may have been even earlier!
Early use of “Xmas” includes Bernard Ward’s History of St. Edmund’s college, Old Hall (originally published circa 1755).An earlier version, “X’temmas”, dates to 1551. Around 1100 the term was written as “Xp̄es mæsse” in the Anglo-Saxon Chronicle. “Xmas” is found in a letter from George Woodward in 1753. Lord Byron used the term in 1811, as did Samuel Coleridge (1801) and Lewis Carroll (1864). (Wikipedia)
Religion was more prominent back then, so blatantly mocking it would cause a lot of social contention. Another thing is that paper or vellum was expensive in history, so scribes would want to save space. Names had abbreviations among other things, not unlike our text-talk today! The word Christ was written as Xp and Xt historically too. At one point, there was even “Xtianity” in the place of Christianity. Strangely, other names that contain the word Christ like Christina or Christopher have been abbreviated with the X too!