Thinking about it, I'm not surprised. Roguelikes lend themselves to short stories. REALLY short stories. A novel-length roguelike story? Wouldn't that be sort of the list of all monsters you killed, with some slight movement descriptions in the middle? Maybe a story-line, not too complex (get the amulet anyone?)
I think the shortness of a lot of stories I've seen is just a lack of ability (or perhaps will) to inject the setting and characters into the writing, focusing mostly on the action. A good Roguelike story, I'm convinced, would need a healthy mix of those. Setting is one of the major keys to the genre, because it's all about the underground complex. Another is strategy, which manifests in what the characters bring with them or find along the way, and even inserting some odd discoveries can provide direction on how to fill in a plot. Items get lost or destroyed, new ones found or taken.
My story is actually the first I've written of novella length (I've done novel length before, and short stories aplenty), so there's definitely room to include a lot of story. But one of the major reasons was that I made one unusual choice: I included multiple characters. Most Roguelikes, I know, are single-player only, just you against the dungeon, but from the start I tried to inject some sense that the ruins could be a real place, that real people would live near and would be tempted to explore. It was sensible to me then that most expeditions would involve multiple people, and having multiple characters gives you the advantages of dialogue, intra-party conflict, and death to flesh out the story. I don't think most fan-fiction writers think to do that with Roguelikes because it doesn't seem proper, but to me it's always been about the setting and the strategy, both of which are easily included no matter how many characters you've got. I ended up sending in a party of 11.
That's not to say that multiple characters are necessary. I could quite easily see building a convincing story around the same plot as Larn, where a father goes to find the potion that will save his daugther's life. Lack of dialogue, though, means that other literary devices will be needed. It'll be rare for a lone character to talk to anyone, except maybe an intelligent creature living in the dungeons. A story like this one would benefit from following the protagonist's survival tactics, learning his state of mind, getting deep into his head.
From what I learned by writing in this genre, I feel quite confident that an entire novel could be built around it. And who knows, maybe a D&D story is the way to go to read more, though I would rather see something with "realism [and] credibility" than without. (One way to do that, I think, is not to limit the story to a specific game.) It's just such a rich trove for fiction, there has to be something good out there.