“Rockin'” has become one of those terms that have come to mean the absence of what they describe, like “extreme” and “perfectly legal.” Anything described as “rockin'” is nearly guaranteed not to rock. Case in point, there is perhaps nothing less rockin’ to do with your New Year’s Eve than to turn on the television and watch other people having a party.
I submit to you that there is a corollary to this.
When an artist creates or participates in a Christmas song, Christmas album, or something else T’is-the-seasonally-themed, that event marks point at which that artist’s career ceases to rock. Christmas music is the shark-jump of an artist’s career; it is the chasm between between the genuine article and the, if you would, crap. This is because Christmas music is both commercially reliable, generally awful and of approximately no artistic value whatsoever. Tastes may vary, of course, but disagreeing with me in this instance means that you’re wrong.