Why do we tell our children the gifts we give them for Christmas come from a man with a beard in the sky? For two reasons. One, the myth of Santa Claus creates mystery around the gifts, like another layer of wrapping paper. Not only is the gift concealed, it comes from someone the child has never met - someone with strange powers of transportation and intuition into choosing (and making) the right gift.
Inevitably, the child finds out Santa Claus does not exist. Are we just being cruel - delighting in the disillusionment of childhood? I don't think so. We recognize on a deeper level that finding out a man in the sky with a beard who does nice things for us (or gives us coal if we are bad) does not actually exist is a good thing - to discover that the gifts we receive are generated from the raw materials around us, and given to us by people who know us and love us.
But we have to remember one more thing as adults. Santa Claus is a facsimile of another myth - a larger man in the sky who dispenses blessings or can curse us. And like a child, the discovery that this is just a story both dispels an illusion and is empowering. We grow up again.
The larger myth of the man in the sky was told and retold for similar reasons we tell a child Santa Claus exists. It helps to create a reward/punishment model to keep us in line, and creates a sense of wonder. However, the sense of wonder at the gifts dispensed from above has had some rather negative side effects. Primarily, we don't recognize the gifts actually come from the raw materials and people around us.
The raw materials that the gifts are made from include...us. We too are resources for others, gifts for others. And when we dissolve, we dissolve back into the elements the gifts of nature are composed of. We don't go back to the north pole on a flying sled. This is the bigger reveal that the myth of Santa Claus is meant to prepare us for.