The eleven notes of the chorus of "Jingle Bells" are like a universal particle of Christmasiness in music. If their Christmas song isn't Christmasy enough, it's always those eleven notes that they turn to. Just tack them on, usually right at the end of the song, and bang, instant Christmasiness. Of all the Christmas standards it is by far the one most likely to be quoted this way, probably outnumbering all the others put together by several to one.
While I wonder why that particular set of eleven notes is singled out amongst all Christmas music, I can't help but observe that "Jingle Bells" isn't even really a Christmas song. Like so many other standards of the season, it's entirely about winter itself, and is precisely as appropriate in February as in December. My absolute favorite Christmas song, "Let It Snow," is another one of these, along with so many others -- "Baby It's Cold Outside," "Frosty the Snowman," and on and on.
Sure, that's a technicality. Those are all songs we play around Christmastime and of which we are usually tired by Boxing Day so we stop playing them the rest of the winter. For all practical purposes they are Christmas songs. Okay, I get that. But I'm not saying "Jingle Bells" shouldn't be played at Christmastime; I'm saying, why is it elevated over all the songs that are actually about Christmas as the single source of the most concentrated essence of Christmasiness, the one everyone always uses to make a song more seasonal, whether the song is actually about Christmas or just winter?