Hi, English isn’t my mother tongue so I was asking myself that question since I first encounted a w/… Back then I was like: “What tf does ‘w slash’ stand for?” And when I found out I was like “How, why, and is it any intuitive?” But I never dared to ask that until now
As a non-Christian, I never made that Xmas connection. It sounds cool, but I was never sure why anyone started calling that (and evidently never curious enough to go looking for an answer or even really ask, I just kinda took it as one of those things that is how it is because people are going to people).
Oddly enough, people who didn’t know that part of the history got angry “they took Christ out of Christmas!” So then people who liked the holiday but not the religion used it to do exactly that. As you say, people people.