Within at least physics, there is still a lot of importance placed on "prestigious" journals like Phys Rev. So it's not so simple. Why would authors trust something published in the "Journal for Comradely Science"? It makes it very difficult to start something just due to the scientific cultural inertia.

Realistically it is 100% possible. But it's the same issue the rest of the working class runs into: insufficient organization. The push for open source in its current form is just a way to make science open without affecting the profits of these huge journals. It costs the author to publish in a journal (which usually means the government allocates x-dollars within grants to pay for publishing). So it's a farce tbh.