I think there's sort of a sliding scale thing going on here.
Start with a nice fluffy kind of rich cupcake with light creamy frosting, made with simple ingredients that you would find in your kitchen (flour, sugar, eggs, butter, real vanilla extract, baking powder, etc). If you have time, fairly standard kitchen equipment, and a little bit of skill, you can make these. Or, you can buy them fresh from one of a growing number of fancy shops that specialize in cupcakes (for a price, and you have to get to the right place during their business hours while you want a cupcake -- and if you live in a smallish town, there's nowhere you can buy them). The bakery probably times their batches carefully and tries not to sell anything that wasn't baked that day.
Okay, so you don't have time to make cupcakes (and you only wanted one or two), and you don't have the time/money/access for really great cupcakes. Next option down: local supermarket. They probably make them on-site, but they have probably "value engineered" the ingredients, "streamlined" the process, and increased the shelf-life of their products so that the curve of taste/texture takes a dive at about the three-day mark instead of 12 hours. So most of the dairy fat and some of the eggs go away, and are replaced by a combination of vegetable fat, and some kind of stabilizer/moisturizer combination (guar gum and stuff) that . . . well, it results in a similar texture to the original ingredients (and takes longer to fade after baking), but the flavor isn't quite right. Oh, also they can try to claim that the reduced fat is better for you (even though we're starting to see pretty clearly that replacing fat with sugar & starch is not the right answer). So this cupcake is similar to one you might make yourself or buy at a nice cupcake shop. And it's cheaper and more available.
Hmm. It's late at night, or the end of a tiring day, and what's available is the corner store / gas station / pantry (last stocked a week ago). The desire to eat one of those kinda mediocre grocery store cupcakes (which you're accustomed to by now, because who has time/money for the real thing?) is pretty high. And those Twinkies are sitting there. They're sort of like grocery store cupcakes. They have almost the right texture (despite having been on the shelf for like, two weeks, and who knows how long they spent on a truck, and in some industrial freezer). The cake flavor is . . . based on flour and fat. The frosting is inside, and that kinda makes sense since it wouldn't have survived the ride if it was on the exterior. Frosting's also kind of weird, but that's the stabilizing and texturizing again (can't use butter, it would rot, can't use most fats, they would separate, it's pretty much just whipped sugar and another of those texturizing agents). Well, close enough to quench the craving, probably.
And of course, there are probably another couple layers in there of degradation, because at least according to the comments here (I haven't eaten a Twinkie in 20 years I think), the current Twinkies are actually just reminders of what Twinkies used to be.
So it's probably just a reminder of a reminder . . . of a really good baked good. It's what's available cheaply and easily. And it's kind of representative of a lot of what's wrong with American food.
Animals (including humans) are pretty good at deciding that what's available to eat is what's good to eat. That's good for survival. Unfortunately, it's also apparently easy enough to trick using modern food science.