...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:
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.