Similar to the Girl Who Ate a Death God, this is a dark fantasy story that is more gritty and complex than most LN fair. It's one of the better LN I've read and it would be nice to see it get a proper adaption.
This is the sort of story that might appeal to people who like stuff like Overlord where morality comes in shades of grey and there is a lot of emphasis on big picture political struggles as seen through the lens of the character's perspective, large scale war and complex world building.
Loved the anime, and would love an official licensed English version for the novels (someone is fan-translating this but would be better if j-novel club did an official English so that I can buy an official digital copy )
I didn't really go there but more about JNC's general taste.
If you ask Sam, he will say older stuff like Outbreak Company, Orphen and any other series we think of ain't really doing that well.
Back to the topic at hand, according to the numbers, older series, non-fantasy, and dark/tragic series ain't what JNC audience finds "interesting."
Even if I find Kokoro Connect, and Outbreak Company are interesting and Smartphone ain't much, majority of JNC ain't agreeing.
Interesting is relative concept, so while you are talking about ain't a thing but that doesn't change how sales here are.
We can agree that interesting is relative, but the question becomes what is being declared as old. Technically, all the series on the site are new to English readers as they're released. It could be assumed that fanlations of a series may impact this since a lot of series have previously been translated in that way. However, if that is discounted, they're all new. If it is assumed that the presence of a fanlation makes the series "old", then the presence of such should be an immediate deterrent from licensing if looked at from a business perspective. Personally, the couple of fanlations I've looked at seemed to be poorly edited machine translations, so I have no interest, but have seen enough mention of them on the forum here (especially in license recommendation threads) to realize that I'm probably in the minority in that regard.
I will agree that isekai/fantasy is the predominant market on the site, but that in itself is a plus for this particular title. However, comparing titles simply because they're in the same niche is a slippery slope. Some titles just don't have a mass appeal, or have aspects of their story which just aren't compatible with a mass audience. To assume that genre or intended audience should guarantee success is like making an assumption that horror B-movies should be reaching the same audience scale/popularity as a major Hollywood release. The story is going to be the deciding factor in success.
Even for non-members, interest in the story should be possible to generate with the first "preview" of a title. If an impression isn't made with that, it's not likely they'll return for the next. In a sense, I guess this could be an unanticipated advantage for a series with an older anime. Anyone wanting to continue the story, assuming they enjoy reading, would be drawn to the title. By the same caveat, anyone that found the anime lacking would be repelled. All the more reason to dislike some of the poor adaptations recently.