Isn't there ever an unhappy ending?

Kurt Vonnegut's good fortune chart found through Google

           I went to the movies the other day and saw "Pitch Perfect". It was a really good movie, but in the end it was predictable: (SPOILER ALERT) the guy gets the girl and the girl's team wins the big competition. The movie got me thinking what if the guy ended up alone? What if the team came in last place? Right now, I can't think of one movie that ends with only unhappy events.
           In class earlier we read a packet called "Here Is a Lesson in Creative Writing" by Kurt Vonnegut. It discussed different shapes of stories. The "good fortune" graph shows the stories that start off with good fortune, and then has some ill fortune in the middle, and they always end with good fortune. After discussing that shape we saw another graph for stories that start with ill fortune and just get worse from there. While talking about these tragic stories, one of my teachers said that these types of stories are not written by American authors. Why is it that Americans don't write these kinds of stories?
          I think it might be because the American public wouldn't respond to them well. Stories with happy endings have hope and stories with unhappy ending just make you sad. So, it makes sense that people would want to feel happy over feeling sad. However I don't understand why that characteristic isn't universal. What is so different about the American authors or the American public?