Because he is a rank and file person who won't behave. His editor sent him a list of reasonable corrections. They did not ask him to resign or tell him he was u

Because he is a rank and file person who won't behave. His editor sent him a list of reasonable corrections. They did not ask him to resign or tell him he was unqualified to make editorial decisions like your version of the story supposes. Instead of applying the corrections or pulling rank and saying that he's the founder and wants his article to be published despite the damage it might cause to the paper's reputation, Greenwald threw a tantrum, flung a bunch of accusations at the editor, quit, and took it all public.