I've also seen something online which is a quote from the program director saying he doesn't want to go all Christmas because of the repetitive element.
(a) All-Xmas is a gold mine for whoever does it, so no way they're not gonna do it again. (b) it can be done without the sort of repetition that most stations use -- playing things like John & Yoko's "Happy Xmas", Feliciano's "Feliz Navidad" (as well as Wham and Mariah Carey) every 2-to-2-1/2 hours is just not necessary given the volume of contemporary Xmas music available.