For one thing, I don't have time to do my LiveJournal!
Seriously, for those who do celebrate this holiday, this may not be as obvious as you think. Or maybe it is--but I'm going to re-cast it somewhat in motivational arousal terms, to explain why some people shop the 24th, and why so many people get unbelievably stressed out. Or, as David Letterman said on his Christmas Eve show in Iraq: ""If I wanted to face insurgents I would've spent Christmas with my relatives."
Why is Christmas so stressful? Sure, it's a time when people feel as if they need to buy presents, and there's often a lot of preparation, but let's face it, everyone complains about how far ahead the "Christmas season" is starting. In the US, some stores put up decorations after Hallowe'en, which by my calendar is 54 shopping days before Christmas--or about one seventh of the entire year.
Here are two related connections: Christmas is stressful because it hits ALL your motives--hard. Observe:
Affiliation: all those family members in town? 'Nuff said! What if they hate their presents? Since I'm so stressed, what if I really annoy someone? What about those old family resentments?
Influence: office parties, also, what if everyone hates their presents? What if I didn't spend enough? What if I spent too much? Have I put up enough ornaments?
Achievement: I've got so much to do, and limited time to do it. And there's no clear marker of "right." What size tree? When do I put it up? How many presents is enough?
A lot of families have traditions that constrain some of these issues. When it works, that's great--a tradition can relieve stress by taking away a decision. If you always use the same artificial tree, then you don't have to buy a tree, set it up, water it, and decide which ornaments will fit. It's a done deal. But traditions can also work against you by demanding work you can't do, which will then make you feel anxious or a failure: "I have to make a big seven-course dinner, because my mother always did." Even if you're at home? Even if you've been traveling the previous three weeks and have no food in the house? Does your spouse even like the seven courses your family makes?
Let's face it: what will make you happier? Slacking off may enable you to actually enjoy the holiday.
And if your family's traditions conflict with your spouse's, that can be MAJOR stress. My wife and I carefully negotiated our Christmas traditions, and it's taken a few years to be reasonably sure we have reached a fair balance of traditions (including some new ones of our own), and even then we check.
Now, the other side: why do some people (usually, but not always, men) shop at the last minute? I spoke to one friend of mine who noted that her husband liked doing it--it was the thrill of the hunt. They were long-married with no kids, so they could manage their own way pretty easily. I thought, hmm. Yerkes-Dodson? The later you wait, the more of a challenge it becomes, and for some people the more interesting, especially if you hate shopping. Then it is about "speeding up until it becomes interesting again," to quote a friend of mine on how he drives when tired.
I have a suspicion as to why men are more often characterized this way, but I won't speculate at this point.
We do our family presents on Christmas Eve and Santa comes for Christmas morning, so we're pretty much on the glide path now...for those who celebrate this season, I hope you do manage to enjoy it!