JSTOR was explicitly a library of public domain works, consolidated in a single place so that academic libraries could access those papers that nobody had an interest in distributing anymore.
It recently added a bunch of copyrighted journals. It didn't have any of those at the time.
I re-read the MIT report by Abelson and it looks like JSTOR was an archive of old scientific articles from many journals, most of them still under copyright by the journal. I'd need to see more evidence that it was public domain.
It recently added a bunch of copyrighted journals. It didn't have any of those at the time.