They are a relic of a bygone era. They made sense when journals were physical publications in the library. Elsevier was the one-stop-shop for all of the major academic journals. But with the internet, they make less sense and kept their position through inertia and rent seeking behavior.
I think (and this is only my honest, outsider perspective) that the issue is, and always was, about trust. As in: who is this dude publishing this paper about high-energy particle physics? I don't know him, so I don't trust him. But I do know about Science, and Nature, and other Journals, so I'm gonna use them. That's why Elsevier and Springer and other publishers continued to exist.
Problem is, science isn't about trust. It's about knowledge, and more importantly, truth. But how do get the truth? Well, there's witnesses, and evidence, and Reproducibility™ of statements to produce facts. Y'know, science itself. If we could somehow resolve the reproducibility crisis of science, I think we would be one step closer to ending the parasitic mono-duo-oligo-whateverpoly of these publishers. Because then it would not be about who I trust to move forward the science enterprise. Instead it would be about facts themselves, and about confirming, via evidence and reproducibility of these facts, that would promote a piece of statement into knowledge. And that is how science should always have been, since the very beginning.
But the reproduction of experiments is a problem in itself, that might be the cause of the 'relying-on-trust' issue. Since not all experiments are a simple ./build-and-run.sh script, and some involve a lot of money (think anything in medicine, physics, geology, oceanography, and the list goes on to ∞), it ends up being about someone that is reputable and reliable that had money and did the experiment and published in some journal that I know.
You can even start a subscription newsletter titled "rtpg's best of Arxiv", containing curated links to a shortlist of the highest quality research you can find. It could become very prestigious for researchers to be mentioned in your newsletter, and your own reputation will hinge on the quality of the papers you link to (and the ones you leave out). Even so, this service still doesn't require that you host or own copyright to those works!
Nor does this arrangement require that any one work be found on only one single curator's shortlist and no others.
That's something worth signing up for.
<https://gowers.wordpress.com/category/Elsevier/>
<https://bjoern.brembs.net/tag/open-access/>
More so for some fields than others: physics, chemistry, and biology are making significant use of pre-publication and open-publication options (e.g.., arXiv, PLOS, PUBMED, BioMED). Medicine apparently less so (closed-access publishers include the New England Journal of Medicine, Lancet, and Nature). For social sciences open-access/prepub options include SSRN, RePEc, and EconStore, but much research remains in closed-access journals.
Law is almost exclusively closed-access, which is problematic in all manner of ways.
Firstly, it can be by providing a good service. Before the war, most papers were published by learned societies and such societies tended to not be very good publishers – they would be slow with long backlogs and unable to publish the volume of papers scientists wanted published at the time. By providing a faster service they could get papers.
Second it can be by offering a service at all. If you have a Springer journal and an Elsevier journal for some field, they can both get papers because researchers need to publish to advance their careers and one journal will not be big enough for all the papers in that field
Third can be from being a preferred choice by being prestigious, which can matter even without impact factor arithmetic – hiring committees made of peers can still know which journals in the field are more prestigious / harder to be published in, and take that into account when hiring. It’s not totally clear to me how to become prestigious. One way is by inertia – if you were prestigious before you probably still are. Something some publishers (Pergamon Press, but maybe others too?) did was owning and dining prominent scientists to get them to sign exclusive contracts to edit new journals. Perhaps this association via the editorial board could improve the journal’s prestige or otherwise get desirable papers in.
It does seem true to me that scientific publishers used to provide a pretty valuable service, and I think if one were in a government looking at all the government money going to the journals via universities, one might be able to feel that the improvement to the rate of scientific exchange was worth it.
It feels that today, a lot of that value comes from various kinds of inertia/lock-in: Elsevier has the papers and scientists must publish in Elsevier journals to advance their careers, which maintains the prestige of those journals and means the publisher continues to have the papers.
The current model for traditional publishing vets each paper that is published; arxive vets each author[1] once, and then their papers can be published.
So, sure, you could be reading the ramblings of a random person, but it is quite unlikely.
I think what is more valuable is looking at the citations to the work you are reading; unless you are reading something very very new, if it is valuable at all it would be cited.
[1] When I last looked at publishing (maybe a decade ago?), arxive was vetting authors, not individual papers.
Yes, tex-savvy authors can do a pretty good job but it's just not the same. That's one reason authors choose to pay the page charges.
Curating is also surprisingly important. Sure, you can often get some author to send you a free PDF from something written 10-20 years ago. But it's also not uncommon for the author to be very unresponsive. Maybe they left academia. Maybe they're lazy. Who knows? But I know that I can't count on getting a free PDF from any author.
They have the power to send their work wherever they want. Really. They do.
The fact that they continue to choose the publishers after all of these years suggests to me that the publishers are doing something that the authors want.
And btw, who do you think would do this work for a fraction of the cost? Are you going to pay them? What if they unionize and demand a fair share of the grant money?
I feel like the Wizard of Oz telling Dorothy she had the power all along.