I see it two ways, and I'm going to speak in very general terms,
A) For the kids, it's the presents and time off school and food and being happy just being kids. But honestly, only for some kids.
B) For adults, it's spending some time with your family and friends and spouse and kids, if you have them. But honestly, only for some adults.
I think the holidays tend to "illuminate" the kind of childhood you had and, in some ways, how it's impacted you as an adult.
The state of the world and the economy are factors too, but you have to remember that society is set up for two things 1) Get us to be good consumers and B) Procreate so we can make more future consumers. It is not socially "ok" to be alone on Xmas. But nor on Thanksgiving or Valentine Day or New Years or any other time either. Society wants you integrated into a family unit so you will spend, spend, spend and spend. Spend to get a commitment, spend to have kids and raise them, spend to buy out your divorce.
Sometimes life is just really lonely. Except we aren't allowed to say it. Especially men. And usually people don't want to be alone because that's when they have to face themselves and deal with themselves. Having "people around" is like a big buzzing sound to distract you from yourself. Or do you think serial monogamists, workaholics and emotionally unavailable people just came out of nowhere?
People who came from solid childhoods with both parents and a stable situation tend to have a better chance at being able to be content alone. Not always an extremely better chance, but I would say the building blocks are probably more likely to be there.
But most people don't come from stable childhoods. Many come from broken homes and broken families. Raised, or not raised really, by people who don't know themselves and never did before they got together and had a kid. People who don't feel like they deserve anything good in life or have the right to be happy that have kids who learn to be the same way. These are the folks that look to have the gaps in their life filled by something , anything - more noise, more things flashing in front of them, more distractions. Or did you think the select people who drown themselves in collectibles, sometimes to borderline manic excess just came out of nowhere? Because dealing with yourself is hard and most people can't do it and mostly because dealing with yourself just really hurts. Because healing yourself and fundamentally changing how you see yourself in context to the world hurts.
And that's why life, not just Xmas, can lose it's "sparkle" sometimes.
As corny as it sounds, true happiness, really does, in fact, start on the inside.
Merry Xmas,
Gekko