The publishers provide hardly any valueHere's an insider's view from having worked the tech side at a small scientific publisher. Prices are too high and the model is flawed [-1] but your opinion is not accurate, the publisher did a tremendous amount of work:
First a distinction, two types of editors: The publisher's editors, each of which handled a batch of journals. The journal editor, who did not actually work for the publisher. The publisher's editors were well educated in the fields they covered, though usually not specialists or researchers in their own right. The journal editors were typically researchers themselves, and being the editor of the journal was not their primary work.
-The publisher's editors organized individual journal editors, helping to find new ones when one left, keeping them on deadline, etc.
-The publisher's editors processed submissions to the journal working with criteria set by the journal editor to perform an initial review for off-topic, low quality, or otherwise flawed submissions.
-The publisher's editors coordinated an enormous network of peer reviewers and the logistics of getting them assigned to submissions and also staying on top of them for deadlines in submitting reviews & feedback.
Other publishing staff:
-performed proof reading & copy editing
-did the layout & type setting
-They used professional color matching labs for all color images, which itself was $100/image (tech for this has probably changed and made it cheaper) [0]
-They managed every aspect of the actual printing of the journal, dealing with printers, reviewing proofs, coordinating a final round of review by the journal editor and authors.
-warehousing copies for expected distribution over the life of the journal, re-prints when something was more popular than expected, and all order fulfillments to individuals & libraries. [1]
-They handled all of the financial logistics, from collecting subscription fees to paying the journal editor and handling royalty fees for decades after a journal was printed & back copies were purchased.
This setup might seem strange, but consider that for the journal itself, the journal editor is often a researcher themselves with very little interest in the mechanics of putting together a publication. They handle reviewing which articles that published and coordinate on the peer review process, and a bit more, but the lion's share of the work of actually turning raw, non-peer reviewed submissions into a printable journal was either coordinated by or directly done by the publisher. All of this cost a lot of money. (Incidentally, the publisher I worked for was ultimately purchased by Elsevier a while after I left, but then Elsevier had to take over all of this.) [2]
[-1] My own opinion is that research funded by the public in some way should have part of the grant dedicated to publication costs. This would keep subscription costs to a minimum and also ensure that not just positive results were published.
[0] Of course this would only apply to printed journals. If you were viewing them online you had to deal with whatever combination of monitor idiosyncrasies and color profiles available, and the difference could be large. It was obvious why they went through the trouble of paying for color matching on print versions.
[1] This was before print on demand was much of a thing. These days it's probably easier to manage
[2] This isn't always how it works. It was where I worked, but for a large publisher like Elsevier there are different models. It's definitely how it works for journals owned by Elsevier. More independent journals may do more of the work themselves, but they may also contract Elsevier to do it. Elsevier may simply license the rights to distribute a journals. But someone has to do the work outlined above.