Those 4 guys in the late 60's who attacked a jewel merchant on New York's West 46th St. on the sidewalk, so they could steal his jewel-filled station wagon, which they abandoned 2 blocks later because none of them could drive a stick shift. Where would I be without such people?
The fictioneer labors under the constraint of plausibility; his inventions must stay within the capacity of the audience to accept and believe. God, of course, working with facts, faces no limitation.
Santa Claus is a god. He's no less a god than Ahura Mazda, or Odin, or Zeus. Think of the white beard, the chariot pulled through the air by a breed of animal which doesn't ordinarily fly, the prayers (requests for gifts) which are annually mailed to him and which so baffle the Post Office, the specially-garbed priests in all the department stories. And don't gods reflect their creators' society? The Greeks had a huntress goddess, and gods of agriculture and war and love. What else would we have but a god of giving, of merchandising, and of consumption?