Yes, I agree employees at Elsevier aren't doing the actual peer review. However, they do critical filtering work before the any journal editors see the paper. See example from Elsevier employee Angela Kerr.[1]
The programmers who think they can revolutionize academic publishing by developing a new peer-review collaboration platform don't even realize that people like Angela Kerr exist. (See repeated disgust in this thread about "peer reviewers are unpaid". That's true but it also makes Ms Kerr's paid work invisible.)
In addition to basic copy-editing, she prevents crackpot articles such as "Darwin's Theory of Evolution is proven wrong by Trump" from reaching the journal editors and wasting their time. (She may inadvertently forward some bad articles but she has enough education to reject many of them outright to minimize the effort by the journal's scientists.)
Administrative people like her cost money. One would have to replicate her duties somehow in the new software platform. That's because the journal editors (scientists) are busy and they absolutely will not want to log into a new collaboration platform and stare at a long queue of unfiltered papers that everybody uploaded. Even though Angela doesn't do the "peer review" per se, the journals still want her to make a first pass cut. None of the ideas I've seen from programmers integrate her function into their model of what peer-review software should do.
With something like Stackoverflow, you have volunteers scrolling through the queue of questions and deleting/editing bad ones so their highly valued experts don't have to waste time with them. That's workable for "programming questions" because they are typically less than 100 words. Even with smaller workload of not reading 20000-word research papers, volunteers still get burned out and quit.
For highly prestigious papers like Nature and Cell that would attract a high volume of uploaded papers, it's very doubtful you'd have volunteers like Stackoverflow to slog through all the junk. Therefore, you'd have to staff up some copy editors and pay them money to do unpleasant work.
The problem is that Elsevier charges an insane amount of money for subscriptions (~$800 million in profits with 36% profit margin). Yes, a new system can charge much less money and be more efficient but you still have to do the work that Elsevier does. The journal editors don't want to do it. The potential software model of synthesizing ideas from reddit+github+dropbox+bittorrent+Sharepoint+blockchain ... don't account for Angela Kerr. Programmers think only in terms of distributing files like pdf and LaTeX. That's why they think academic publishing is a solved software problem and not a human effort problem.
>It should be possible to coordinate journal publication through a software platform, replacing the publishers without affecting the peer reviewers or editors.
The software platform can replace Elsevier in particular, but it can't replace the fundamental "work activity of a publisher". Angela Kerr (or whoever employs her) wants to be paid to do the unpleasant work that journal scientists don't want to do. And she doesn't want to be paid in reddit-like "karma votes" or github-like "stars". The new system can pay Ms Kerr less money than Elsevier (and hopefully pass those savings on to subscribing libraries) but let's be clear that the journal scientists absolutely do not want a new software platform without her.
[1] https://www.elsevier.com/connect/confessions-of-a-managing-e...