it's probably because santa is from the northpole, the northpole is cold (and probably has a lot of snow), and all the children are told that he uses a sleigh, so they just pass it on from geniration to geniration that santa uses snow to get around

that, or frosty the snowman said so. lol

why do harry potter and friends use the hogwarts express. they are magic. why can't they just get their through the fireplace