It's not compulsory and not everyone who takes part has been soaked in booze all December?
For me it's a bit about re-setting good exercise, eating and sleep habits, and a bit about saving some money while there's not much going on anyway (I like good wine, and good wine doesn't always come cheap).
I'll be making an exception next week as we have a wine-pairing dinner pre-arranged, but probably won't dive straight for a bottle come 1st of Feb either.