@Kin_tin Because the story is being hard carried by the illustrator. If you actually strip Solo Leveling down to its elements it's a pretty basic power fantasy. Every character is paper-thin, the sole purpose of the world is to prop up the MC.
Though I haven't read the source material I'm guessing it's standard web novel fare, hastily written, barely edited, with prose that makes you want to gouge your eyes out with the nearest sharp object.
You ask why the author can't do anything about the plot when the answer is pretty simple, he (I'm presuming the author is a he) is not that skilled and so can't really create an engaging narrative.
The art is god tier for a webcomic though, all props to the illustrator.