https://en.wikipedia.org/wiki/Copyright_policies_of_academic...

That's changing, and many journals are moving to open-access policies, but it's slow, and the most prestigious journals often have the least incentive to grant authors published in them copyright of the work.

(There's something fucked up about authors transferring copyright of publicly-funded research to private entities: if the public funded it, shouldn't it be owned by the public in the first place, i.e. public-domain? And if it's public domain, then this whole issue goes away and neither the journal nor the author has the right to restrict access to the research. But this is one example of the capture of public goods by private entities. Hell, maybe this is why a good swath of America wants to de-fund science any chance it gets, when the result of their funding just gets captured by private entities.)