Boy, that's the truth. I don't get it, either -- story is always highly emphasized in film school, but you must not be able to teach it because the words fall on deaf ears. When I was watching the screenings of thesis films, most of them were just boring.
Having seen a lot of high quality student films in the last year and a half, I've noticed that the overriding theme in most of them is usually very depressing. I have to go back a ways to remember the way I was when I was that age, but as I recall, your early 20s are usually not the happiest times of your life, especially in today's world. However, if I were teaching a screenwriting class today, I would probably try to emphasize that a positive message is not always something to be avoided. Write what you know is always good advice, but one must also keep in mind that the viewer of your finished piece is not always going to be as depressed as you are. And the visuals often suit the mood - dark, dingy, dirty, depressing.