The usual brainrot Nihongo story telling
It's because authors are physically incapable of writing about characters that are more intelligent than they themselves are.
That's the line that separates professional authors like Tom Clancy and Sir Arthur Conan Doyle from WN writers.
And most of these manga are adapted from WN. Which are posted without any editorial review by amateur novelists.
I enjoy reading WN since it allows more author freedom, can watch story mature -- but then you run into speedbumps like ^^this^^.
At least, not without a large degree of background research and planning. Even then, comes off as ham-fisted. Since many authors resort to cheap hacks like "sequential publishing meaning forgetting plot elements, then suddenly inventing them from offscreen as retcon".
Versus "having an idea in mind, polishing story over multiple complete manuscript drafts, then presenting all hints to reader, but then drawing established lore together later, as climax".
Same way a clever reader can solve Sherlock Holmes books reading along, and not being "bomb-dropped an offscreen plot token in the final chapter" like Detective Conan.
There are a few "debuted" WN authors that are really, really good at what they do. And they know to stay in their own lane/genre.
"The Old Knight of a Frontier District" (Bard Loen) author ShienBIS (支援BIS) for historical high-fantasy.
"Only I Know This World Is A Game (Neko Mimi Neko) author Usbar (ウスバー) for video-game tabletop isekai.
Usually as WN -> LN -> Manga -> Anime, they progressively receive editorial review to polish the story by field professionals.
Therefore, I blame the LN/Manga editor reviewing storyboard for failing to knock off some of those "amateur WN" rough corners.