I don't think its right to say they add no value. They definitely don't add value anywhere near what they charge (clearly based on their profit margins) but they do provide a service (albeit often minor). They coordinate reviewers (who they don't compensate), certain journals (Nature and Science in my experience) provide typesetting and editorial service beyond just basic copyediting, they provide a website to download the content.

I'm in no way saying these services couldn't easily be replicated at a much lower/negligible cost but they do provide a service.

> They ... provide typesetting and editorial service beyond just basic copyediting.

Not necessarily. For-profit publishers today – perhaps more often than not – expect the unpaid volunteer editors of the journal to do any typesetting or copy-editing, and then just send the publisher a camera-ready PDF to print.

Minor correction: many publishers don't even coordinate the reviewers. That's usually left to editors. Editors are generally unpaid, or are paid some trivial insignificant amount.

Additionally, I am a member of several societies who have outsourced their journal publication to a commercial publisher, and who use the money from those contracts to pay for society activities like travel scholarships, etc.