Gunn was fired from his role as the director of Guardians of the Galaxy Vol. 3 last year, and while most reports seemed to claim that Gunn’s script would still be used, that was never confirmed, and even if it was, it’s unlikely it would have been presented exactly as Gunn would have wanted had somebody else directed the movie.
Of course, the fact that James Gunn spent a year making Guardians of the Galaxy Vol. 3, makes the fact that we might have never seen the movie that much more upsetting.