Christmas is a European pagan tradition, really we base our holidays around seasons of which due to the importance of them also feature many religious events.
Except for like all the places still celebrating Yule, imbolc, halloween. If Christianity never genocided its way across Europe, we’d still be celebrating at these times with many of the same customs.
Plus if we let the Christian’s get away with stealing everything, we’d have nothing left.
But you’re right, we can do more to remove religion from government.
I'd argue the reason it's still celebrated is capitalism. Easter is more important in most Christian traditions than Christmas, but less celebrated in society. Why? Follow the money trail. Ask Coca Cola, the modernizer of Santa Claus.
On the other hand its turned into a decedant festival of feasting and alcohol so the pagans kind of won on that one. Which is also the reason for celebrating it for all the non-christians that do.