Retailers want to play Christmas music to encourage shopping, but only secular music to avoid causing offense. If you look at all the most popular Christmas songs and take out any that with religious lyrics (Silent Night, Joy to the World, Oh Come all ye Faithful, etc.) you'd be hard pressed to put together a playlist longer than an hour or two.

An employee working an eight hour shift will therefore hear the same song a minimum of four times. In my experience it's closer to six, but we'll be conservative here. That means Mariah Carey is telling you that you're all she wants for Christmas at least twenty times a week. Most stores start up the Christmas music in early November, but we're being charitable and saying the music will be playing from Thanksgiving through the week of Christmas.

The TL;DR is that your average full-time retail worker is going to hear the same few Christmas songs a bare minimum of 80-120 times during the busiest time of the year. That figure doubles in a worst case scenario where a one hour loop is played starting after Halloween. A ton of people have worked retail at some point on their lives so while you might not be the only one who likes this song you might have a hard time finding people who don't have a knee-jerk resentment towards it.

There's a reason this song is played a lot at Christmas: people like it. It's just that the people who don't like it really don't like it, probably due to how much it gets played.

Am I the only one who likes this song?

Not the only one but it's not a very good song. I liken it more to set dressing than an actual piece of music.