Are you sure the rule wasn’t “don’t publish something only proof-read by the author?” The best journalists I’ve worked with do extensive self editing. Then they

Are you sure the rule wasn’t “don’t publish something only proof-read by the author?” The best journalists I’ve worked with do extensive self editing. Then they file their copy to an editor. Also, journalists work in a different context than other writers. They write for publications with people on staff specifically to edit their copy. Someone writing a blog post, internal company memo, personal essay, documentation, etc may not have access to a paid editor or time to wait on volunteers. Definitely a good practice to get someone else to read something you care a lot about or are getting paid to write. But there are lots of things (arguably!) that fall short of that.