Even the copy editors do little work - they always are very insistent upon the author themself working through all of the style guide to make sure it conforms.
I think the main work they do is to lie about accepting LaTeX and scraping the PDF output instead so as to introduce new errors into articles.
Bean Counting. Captive audiences are always at risk of extortion.
> Aren't they just hosting some pdfs
The internet has been happy to provide that particular component of their empire for free.
> keeping editors on staff to look over the papers?
That's mostly outsourced (for free) to other researchers.