Can you elaborate? Do you mean curating papers via pull request? If that's your question, the answer is that there's absolutely nothing in the way technologica

Can you elaborate? Do you mean curating papers via pull request? If that's your question, the answer is that there's absolutely nothing in the way technologically: academics could easily form shoestring "journals" around a github README files with links to arXiv. As others have said, the real issue is historical: for better or worse the currency of science is still peer-reviewed publications in prestigious journals, and a lot of those journals are still owned by Elsevier. Obviously this is starting to change, but old traditions die hard.