....which is?
It depends how far back you want to go, but the religious reason is not the original (ymmv) and only really relevant to some.
...and, of course, the religious reason is why we celebrate
Christmas (the clue's in the name). It might not be the reason we have a party in mid-winter. There's a decent article looking reasonably dispassionately at the historical evidence and squishing this suggestion:
....or a religion superimposing their beliefs on an existing solstice festival is a good way to try and convert the local population and with less than 1 in 20 going to church, I'd say we're not much of a Christian country. The original meaning of Christmas? Ask how it was celebrated in the many hundreds of years prior to the Church pretending it is actually the birth of Jesus and ideas of a party, eating, drinking and exchanging gifts becomes more authentic
here:
https://www.biblicalarchaeology.org...w-testament/how-december-25-became-christmas/
TL;DR? The feast of the nativity on December 25th is well attested at a time when Christianity wouldn't have wanted to associate itself with an existing solstice festival, whose date is apparently less well attested. An alternative explanation to do with celebrating the birth 9 months after the conception exists and is more credible given what we know about the mind of late antiquity.
And you've cherry-picked the least favourable statistic - 60% assert a Christian identity, and as anyone associated with Christianity will tell you going to church is not the marker of a Christian identity these days (if it ever was). Oh, and "many hundred" is 300 at most -
Christmas (as I said, the clue's in the name) is a Christian festival whose date was settled by the early 4th century CE.
Midwinter parties no doubt go back a lot further, and many of the traditions now associated with Christmas have no doubt been borrowed, but
Christmas (the clue's in the name) is inescapably Christian.
