Why not Christmas,, you ask. Because,, at the time of Jesus, and even after as the Catholic church adopted pagan traditions to their practice of christianity, The practice of celebrating the birth of gods was a principle aspect of pre-christian practices and none of those gods that they worshiped had the capability to do what the Son of God was about to do. His mission was to stands-apart from those traditions of those time, in the same way that Christians are supposed be seperated from the ways of the world.
Jesus tels us to "worship him in spirit and truth". So if we are to take him at his word, we have to learn the truth about what he was correcting in the ways of mankind at that time. They were heavily bound by fear in their rituals to gain the favor of the planetary gods which had in former time brought great destruction upon mankind. A hint of those natural factors is seen today but these modern event are of far-lessser severity because our solar-system has settled into a reduced-interactive condition.
This is a matter of understadning what was being celebrated at the birth of the gods. Their celebrations are tied to the activity of planetary bodies as they were born, moved about in the sky, and engaged in conflicts with other celestial bodies during the periods of celestial chaos that disrupted our planets former condition.
The beginning of the myth-making period occurs early in the biblical story and is wrapped into the creation story's final phase of being driven out of the garden. Numerous catastrophic events were described in the Bible but are not as detailed as if viewed from the mytho-catastrophic records contained in mythology and legends involving Kronos, Zues, Aphrodite, Jupiter and many others. Those legends describe the celestial chaos and were of natural factors. The creator, Jesus is of the spiritual realm and has power over the natural realm, and his mission was to draw mankind back to the Father, creator through a spiritual relationship that did not involve any of the factors in nature which had been assigned god-ship by mankind because of the threat they posed to mankind. This is probably why Jesus did many miracles involving control of the natural world, order was being restored and old factors were to passing away.