Let's just throw out a little scenario here:
Say there's an English assignment. It's a quick one, a one-pager. Prompt: Pick an image from our illustrated edition of Beowulf and talk about how it enhances the literature. I take the assignment lightly, write a seriously snarky essay about how the whole concept of an illustrated edition is ridiculous because the images aren't even remotely related to the text. Thirty minutes, bam, I'm done. I get a check-plus (these college grading scales, they're intricate), a few stray exclamation points, some checks, an "excellent voice," and a "good!"
Now let's say there's a longer assignment. Four or five pages. Crazy open-ended prompt about why literature is meaningful. I write an outline. I find evidence. I give some cute commentary. I take a risk, throwing in a cute line about Athena's funny sandals. It's some serious effort. I get it back and get the same grade as roughly 85% of the class...coincidentally, it was an 85%.
No big deal, I can handle that. But why is it that the quick little things that don't count for much of anything turn out so much happier than the clunkers that take up so much time and make up so much of my grade? It just doesn't make sense. Then again, neither does half the stuff that comes out of the man's mouth.