I didn't exactly mention anything about quality, but engagement have everything to do with quality, narrative, advertisement, attention, etc is a whole package anyway, if your story fail at one of these points or at everything while you were trying to get an audience or aiming at your specific one to sell it to, then is a failure, it didn't engage with whatever audience it was trying to get, and this apply to every other LN that have failed, Raising Kids played it fine and got its audience and have maintained it for years, MotoMusu didn't retain it because no one engaged with the story, LN world have always been more ruthless than manga as they are way more prone to getting axed, because most of these stories are basically coming from the equivalent to fanfiction or wattpad so there is a more fierce battle once they get published as LN (and while syosetu isn't the old jank website, they still try to bait with the titles), doesn't help that the author doesn't fully commit to its own stories, and aside LN are LN, and cars are cars, thats the dumbest shit you could come with
Manga is skipping around for more reasons than the story being "super dark" at some points, and that have more to do with the current status of the artist for some years now, long hiatus + condensed story kept her from getting exhausted, otherwise the story wouldn't move at all