I agree with you. Usually, stories with protagonists who act like this are the fault of the author's incomplete character development. They don't know how to develop the protagonist anymore so what do they do? They either nerf the heck out of the protagonist or change their personality completely in order for him or her to, "develop" as the story gets longer. This is quite common in the writing world. Unless they specifically show how the character had changed, such as being influenced by peace or friendship, just know that they are running out of ideas for how to develop their character more. I understand that it is quite annoying, but writing takes a lot of mental stress and planning. For authors who are genuinely serious about their story of course. Not those, "Court Death!" kind. You know what I mean?