Why do the chads celebrate Christmas?

It is a public holiday that is celebrated to celebrate Jesus' birth.

The celebration of Christmas in late December is certainly as a result of pre-existing celebrations happening at that time, marking the Winter Solstice. As Christianity began to take hold across the Roman empire and beyond, the date of when to celebrate the birth of Christ became a bit of an issue, with several different dates proposed. It wasn't until 350 AD, when the then Bishop of Rome, Pope Julius I, fixed the official Christmas day on December 25. Unfortunately, Julius, I didn't show his working out on how he reached this date; some scholars later suggested that it was calculated as nine months after the Annunciation (March 25), when the angel Gabriel is said to have appeared to Mary and told her she would bear the son of God. Whatever the reasoning, it is clear that, just as key pagan sites were being chosen for new churches, so too the date was chosen with the intention to catapult Christmas into becoming a major festival by placing it over the pre-existing pagan festivals.