Because to do it at any other point of the year would detract from the occasion. The reason why we do certain things only at Christmas time is because that what makes it special.
Personally I can't wait for that massive, tummy-busting plateful of poultry and pork meats, stuffing, gravy, sprouts and ton of vegetables.
Just don't expect me to eat any puddings, cakes or sweets for the rest of the day.

