Fantasy stories tend to get stuck into a particular kind of trope, namely defining the world in which they take place. As a nascent writer (I'm not very good at long form stuff, and some might argue that my short stories leave something to be desired as well) I like to think about these kinds of things. This isn't really related to D&D, save incidentally, but is more about the nature of fantasy.
So, anyhow, fantasy stories tend to take a world-definitive approach. When you read a fantasy story, you probably aren't going to read a second one set in the same world: the world has been defined and its heights and depths clearly staked out. If there are more stories to come, they will be set in a future time when the world has changed because, let's face it, you've seen it all already.
Fantasy, unlike most other genres, often seeks to exhaustively define every aspect of its setting. The heroes go to all the places and meet all the people. Every major event is incorporated. Everything changes at the end. Perhaps this is a hold-over of the mythic hero-journey. Here's what really interests me: most other genres of writing don't do that.
You wouldn't read a murder mystery and think "Huh, I've seen everything there is to know about earth now. I've pretty much exhausted all the places in it." That's because murder mysteries don't seek to define the entire planet, they simply exist within it. Fantasy tales are generally about big, world-changing, sweeping events. They must by their nature define the world they exist in both because their plots are about changing everything and because the reader doesn't really know what the setting itself is.
When I was in high school, I read H. Beam Piper's "Little Fuzzy" and rapidly realized that he had constructed an entire setting and that there were multiple stories (completely unrelated) that took place in it. It brought to mind the Asmiov I had read when I was little. Unlike, say, Dune, the stories weren't all-encompassing about the highest level of power. They were on a human scale, about human people that did human things. Many stories could co-exist within the same setting.
I always wondered why people didn't do that with fantasy. I suppose that's not why most people actually bother to read fantasy, but I have tried (unsuccessfully so far, but I've still got health and life left in me to try again) to accomplish just that task. Where are all the stories about a knight-bachelor who doesn't change the world, but gets caught up in local politics? Where are all the tales about a wizard who doesn't go on a mighty quest to save the very world he lives in, but rather finds and loses love?
I suppose I have become interested in what one could consider cross-genre works, in which the element of the fantastic is a backdrop for other elements. Is it an inextricable part of fantasy that the heroes must retrieve a magic thing and do a magic thing to a magic man in order to prevent all the magic from going away? Or can there be fantasy that explores ground-level human themes rather than epic and mythic ones? If there can, is it worth writing, or would it be boring?
These are the kinds of questions that plague me at night.