The Christmas 24/7 format is a recent development, starting perhaps 15 years ago. Before that we would simply mix in the Christmas tunes with the regular format until Christmas Eve, then go all Christmas til around noon on 12/25, pulling whatever we could from Christmas albums collected over the years. The Christmas songs in regular rotation were the usual classics, the Crosbys, Coles, Williams, Mathises, Presleys, Sinatras, Beach Boys and the like, and every station had a few of their own that they would pull out of the box, but the usual pre-Christmas Eve rotation was never more than a dozen or so songs that were tried and true. There were never any new songs.
In the 1980s some stations began balking at playing artists they would never ordinarily play, so we began to hear Christmas songs by contemporary artists on those "Very Special Christmas" CDs. Some of these were good. Some were awful. The better ones rose to the surface to be played along with the aforementioned classics. And some new ones come along from time to time. Josh Groban's "Oh Holy Night" has rightfully become an instant classic.
Yes, disc jockeys play what comes up on the computer, just as we played what came up in rotation when we were playing vinyl. So what else is new. Some people dread playing Christmas tunes, but while there are some songs I detest, I generally enjoy them. When else am I able to play some of the greatest performers of the last century, in their prime. The listeners love it and are happy about it. It's only about 3 weeks out of 52. What's the downside?