Having seen this last night I did ask myself the same question. The answer I came up with was that while it was set during Xmas, Xmas was not itself an essential plot point. It could have just as easily been set a few weeks before or after and still worked exactly the same. The Xmas setting was unusually prominent, though. You wouldn't get a holiday-period-centric film released away from the specific holiday (I'm thinking Hop, Valentines Day, Arthur Christmas).
I do wonder, though, if it being set during Xmas didn't actually add anything to the film then why bother at all?