For me Christmas is a season. I like the decorating aspect and love to see the decorations around towns/shops etc.
We do two Christmas markets and I do a Christmas day out, this year it's going to be a stately house.
I don't see how considering it to be one day, works. I'm in my 50's. We visited wider family once the schools had broken up and on Boxing day and the following week. That's always been a tradition.
I don't believe in God etc, but my GM and DH was Catholic so I've carried on observing the Liturgical calendar. The Catholics certainly know how to do bells and whistles!
My natural garden decorations stay up until Candlemass. That's passed on by my Presbyterian Father.
Christmas might be about eating and drinking for one day to many, yourself included, but for many of us it's a celebration, which includes reflection, giving thanks and being surrounded by as much sparkle as possible.
"but it was faintly depressing that people really buy it all"
People don't buy it all. Different people buy want they like/need to make their home as they would like it to be, for our biggest cultural celebration of the year. I don't eat processed carbs, I could be saddened by the choice of bread, a Vegan would say that the animal products aren't necessary.
But we have the privilege of choice and autonomy.