Because Greenwald helpfully published his correspondence with his editors (
https://greenwald.substack.com/p/emails-with-intercept-edito...), as a former journalist I can tell you that the term-of-art for that is "editing," and that this is precisely what editors do every day for every journalist (especially in the better quality organisations). And yes, in many cases editing might reflect the biases of the publication. Editing in the WSJ has a different ideological bias from editing in the NYT. You can think it's bad, and you can even call it censorship if you like, but just so you know, when journalists say "editing," this is the thing they're referring to.
This is why many professional journalist were peeved with Greenwald when he presented the exact same experience all journalists face every day as a normal part of their job as censorship. I guess editing is a censorship of sorts, as is code review and manager approval, but just as programmers say "code review" when they mean that particular kind of censorship, journalists say "editing" when they mean the very ordinary kind of censorship in that correspondence between Greenwald and his editors. When you get a job as a writer, you accept that the editors will "censor" you, because "censoring" is their job, and "being censored" is a part of yours. Like countless journalists before him, Greenwald wasn't happy with the editing his piece received, so he left for a venue with editing that's more to his liking, which in this particular case means virtually none.