A couple of reasons. In Ireland Christmas day is one of only two days in the year where pubs are shut, so it was never there for me as an option - it always seemed strange to us to see everyone in the English soaps spending Christmas day in the pub...just like they do every other day of the year.
well most pubs used close here as well too and many still do but if the clientele is there then i can see why they might want to stay open
Also, even though it's been available for me in Scotland for many years, my view is that it's a day to be spent with family, not getting sloshed with mates. As I said, you can do that any other day of the year.
Each to their own of course - was just saying that in my view, it's something I find unappealing and to me it wouldn't feel right to be sitting drinking in the pub on Christmas day while my wife and children are at home.