I have edited journal articles, and yes, they are generally "poorly organized, full of citation errors, full of grammatical and spelling errors, etc." It's a lot of work to turn a crappy first submission into something that's readable.
But I did all of my journal editing as a grad student in college. Technically, it was my advisor's job to do it, but he was too busy with non-mundane things, so this kind of work got passed off to his students. None of us were paid for the work, of course. It was just understood that you do it because you have to (grad students need good recommendations, and advisors to those grad students need to play politics with the journal committee). As far as I can tell most editing for most journals is done for free by various university professors and (mostly) their students. More prestigious journals like Nature and Science probably have their own editors do an addition pass after this, but most don't seem to do that.
It might be different in some fields, but that's how it works in my field (mechanical engineering), and it seems to be that way in other engineering fields as well.
The fact that the journals might be edited for free by grad students and professors doesn't mean the results should be freely available. Many journals are run by universities, and those fees go back into the universities that ultimately pay those grad students and professors.
But I did all of my journal editing as a grad student in college. Technically, it was my advisor's job to do it, but he was too busy with non-mundane things, so this kind of work got passed off to his students. None of us were paid for the work, of course. It was just understood that you do it because you have to (grad students need good recommendations, and advisors to those grad students need to play politics with the journal committee). As far as I can tell most editing for most journals is done for free by various university professors and (mostly) their students. More prestigious journals like Nature and Science probably have their own editors do an addition pass after this, but most don't seem to do that.
It might be different in some fields, but that's how it works in my field (mechanical engineering), and it seems to be that way in other engineering fields as well.