Persistence makes good reporters. The most persistent get caught up in chasing facts and miss things, make assumptions, and simply leave things out. Their sentences may contain ambiguities, lapses in cultural awareness, misspelled names, etc. Some simply do not make sense. Editing serves the readers' need to understand information.
Good editors think on two wavelengths.
They read like a journalist, like a news junkie who knows everything, catching errors and stylebook lapses. They also read like the general reader, who is smart but doesn't follow news the way we do. They look for papered-over cracks, omitted contexts, and simple failure to explain. Editing also makes the story read well, encouraging readers to learn more than a headline and a lead. Reporters think it's because editors spend so much time in meetings, and they' re partially right.