>>281759994 (OP)
If you want an unironic answer, its purely because the adaptation didnt suit the IP. This manga is "hype moments and aura" incarnate. The character writing and plot are all subpar, but it's carried by its humor (at least earlier on), creativity, and the weekly dose of "that" panel.
The anime fails to deliver on these because the manga is better at delivering the comedy, it insists on copying panels to replicate the big moments in the manga, failing to understand that its not as effective to do this in a different medium. The animation in general wavers between mediocre and decent which is not enough to elevate the hype moments and aura mentioned earlier exposing the bare bones plot and characters on full display.
Basically, it took the manga, and adapted it to an anime that removes the main appeal of the story in the first place, making it seem undesirable.