Why Do Some Anime Adaptations Ignore Source Material?

gamerant.com:

One of the most frustrating experiences as a fan of anime and manga is witnessing what can only be described as a bad adaptation. Naturally, these things are particularly subjective; however, from the subjectivity of most fans, especially veteran fans who have had the misfortune of experiencing this at various points in time, the biggest crime of anime adaptations is straying from source material when such material exists.

Titles that will come to mind are the Shounen giants Naruto and BLEACH; however, these suffered a different kind of adaptation curse. The worst ones are the ones that have stories that, again, from the subjectivity of many fans, are brilliant works of art that the anime adaptation simply does not reflect, nor retell. The anime adaptations of fan favorites like Tokyo Ghoul and The Promised Neverland had brilliant first seasons; however, something unfortunate happened in their sequel seasons: they strayed from the existing material in ways that were no longer reconcilable. Why does this happen?

The Promised Neverland: Should Some Anime Stay at One Season

There are various aspects to the adaptation of manga that fans are generally not very aware of, particularly, the involvement of the original author of the IP. While some adaptations suffer due to the necessary invention of storylines and plot that does not mesh well with the pre-established rules of the franchise at hand, others suffer simply due to decisions made out of a desire for better business. Sometimes, these changes are made with the full involvement of the original author, and sometimes, the change was made by them personally. Tokyo Ghoul √A, otherwise known as Tokyo Ghoul Season 2 was such an adaptation.

Series author Ishida Sui desired to make