The copyrighted journals do a terrible job curating articles, something which has been demonstrated repeatedly by people who managed to get utter nonsense through the peer-review process. I have seen Springer editors introduce spelling, grammar, and factual errors into published papers. Never in my career have I seen an academic publisher add any positive value to any part of the research process or community -- at best all they do is put their own worthless name on a journal, and at worst they have negative value.
University administrators, grant-writing bodies, and others pressure professors and graduate students to publish with specific publishers. It is not because those publishers are more trustworthy; it is simply inertia, institutional tradition, and credentialism. It is the same attitude that leads some companies to turn away candidates who never completed a bachelor's degree. To give an example of just how bad this situation is, we sometimes hear complaints about people citing the IACR eprint version of a paper rather than the "officially published" version -- not because they are any different, nor because there is something better about the official version (in fact the eprint version typically includes details that are absent from the official copy), but simply because European universities use citation counts to judge professors and only consider citations of articles published by specific publishing companies.
Academic publishers have raised their fees even as their costs have greatly declined. The number of journals that are actually printed and distributed on paper has been shrinking, and the cost of distributing over the Internet is almost a rounding error. Yet in that same period of time the publishers have increased subscription fees to the point where some university systems could not justify paying for the subscription. These companies have outlived their usefulness and they know it -- now they are trying to extract as much money as they can before the business model completely fails.