One of the main reasons was the art style. I just did not like it at all. I was hoping for it to grow onto me as the series went on but it never happened and it was a constant source of annoyance detracting from the story. However, many people seem to like the unique style so it might be just me so I would suggest giving it a go. Also, despite the art style being bad the animation was a bit better and many scenes rolled out quite nicely.
Another reason was the characters. I just did not connect with the main character at all. Despite him being quite OP on a physical level, his personality was something I could not stand at all. He is very unemotional and just lacks any resemblance of common sense which makes him just frustrating to follow. The arbitrary restrictions of not using his powers on others imposed by his master also just felt very silly.
Regarding the story, it felt very episodic (maybe it was the intention) as opposed to there being a real plot behind it. I also did not like the exorcist element at all a) because it is a very lame concept in the first place imo and b)there was no uncertainty about any encounter ever since the viewer always knew that Mob could take care of the situation
