Because reindeer need their carbs, too
Julie's family doesn't stop with cookies for Santa:
We make reindeer food for Santa's reindeer to snack on when he stops at our house. In a bowl, mix rolled oats, glitter (this is what helps the reindeer fly), cookie sprinkles and or sugar (for flavoring), and baby carrots ('cause they need their veggies). We then take this and spread it in a line for the reindeer to eat while they are still in harness and Santa is in our house. Yes...the reindeer (or rabbits/racoons/possums) really will eat this stuff and my kids get such a kick helping Santa feed his reindeer. My oldest daughter races outside to make sure the reindeer ate before even looking at presents.
My only suggestion would be to exchange the glitter for sparkly sugar if you actually put this outside, as a) who knows what glitter does in the tummies of wildlife, and b) at the very least, it will remain on your lawn or sidewalk.