One of my bosses plays Christmas songs all year long. I may be the only one there who gets it. I've been playing them since October. Last year, I went as far as to attempt to write one of my own (with a little help and inspiration from Franz Gruber).
Most carols' melodies are timeless. They are usually easily transposed and best of all they beg for harmony. Some of the first songs a child learns are Christmas (or other holiday) songs; even non-musical families sing during yearly, family gathering type holidays. The songs become a part of you, ingrained into your very being. Even if you hate them, you can't forget them. They are as insidious as an infectious pop tune. So give in, indulge in the guilty pleasure. "Because you need a little Christmas, right this very minute. You need a little Christmas now."