Many good reasons.
First, once you start celebrating Christmas, you are firmly against the washtowel teachings. You are now worshiping the sun, despite that they have told you how wrong it is. That is enough for a lot of people--once they get the Christmas tree up, they are pretty much done believing in the washtowel.
Also, why do so many worldly people celebrate Christmas, even atheists? Because it is so much fun, especially for children. It is a day set aside to enjoy one's material blessings, to enjoy the lights and sounds, and to practice peace. The "hassle" is part of the fun--it's only when one goes beyond one's means that it becomes a hardship (and donating to the Worldwide Pedophile Defense Fund or doing field circus beyond one's means isn't?). As for the seeming waste of time, it is not wasted if you enjoy the shopping, the lights, the music, and preparing by decorating the house. Tradition is worth something, especially if it sets one year or portion thereof from another.
Yes, it does consume time, energy, and money. But, honestly, how much time were you spending while knocking on doors? Suppose you were to spend all that time Christmas shopping instead--you could have enough presents for the whole town or city block in that amount of time. You could decorate a whole city with the amount of time it takes to do field circus that year. And, the gas you waste, donations to the Worldwide Pedophile Defense Fund, suit dry cleanings, postage stamps wasted on letter writing drives, eating on the run, and so on--now that is a waste.
