The major drama at the climax of the film centers around whether Santa's sleigh is going to be able to fly without the engine that's been keeping it going all these years. See, without the engine, the sleigh has to rely entirely on the magic of Christmas cheer to power it around the world, and according to the Clausometer, there's just not enough Christmas spirit to do the job.
But that doesn't make sense. This is a world where Santa Claus is 100 percent, actually, factually real, with a toy factory at the North Pole staffed by cheerful singing elves, a talking snowman, and everything that goes along with him. He brings presents to the good children all over the world, which means that there's no disillusionment or disappointment from kids who didn't get what they wanted on Christmas morning. We also know from the movie that getting a present does in fact increase your Christmas spirit, as Michael, Walter's other son, boosts the Clausometer a little bit when he gets the skateboard he's always wanted. So if Santa and the elves have been doing their job — and as far as we know, they have — then there should be more than enough Christmas spirit to go around just from that, let alone all the general feel-good sentiments of peace on Earth, goodwill, hot chocolate, etc.
Maybe there's a reason for it, though. It could be that this was just a abnormally bad year for the Christmas spirit for reasons that have nothing to do with Santa. Let's see, this movie takes place in New York, and it came out in 2003 ... was there anything that happened in the early 2000s in New York that would've been catastrophically depressing?
