Sharing your own papers is nice, but it's also safe. It's not really challenging the status quo.
Edit: I overstated my point. I don't know that "most" papers are already available; it certainly varies a lot by field. I kind of doubt that many #pdftributers are people that weren't previously sharing their papers, though.
TBH, historic papers are not that interesting anymore, since the most important ones are cited in more recent research. It's the cutting edge research where it's more annoying. What's more important though is that closed-access is depriving science of the ability to use automated tools for textual analysis. I hope this unfortunate event will motivate more people to realize that having unrestricted access to scientific results is an extremely important issue.
Perhaps one of the reasons for the difference between fields is that, at least in astronomy, our journals are supported by the professional societies, like the American Astronomical Society, and not run explicitly for profit.
I should also add that in astronomy, the authors pay a significant amount of to the journal when a paper is published. It is usually in the range of about $100 per page.
And Wikipedia would kind of benefit from the historical stuff.
> There are actually underground websites for searching
> paywalled journals through proxies.
I left academia years ago but continue to (try to) do research. Resources like scholar.google.com can often help find a free-to-read version of a paper, which is great. But access to a single key paper can make or break your progress. I've personally dropped many, many hours of work because of this problem - I couldn't reasonably access key literature that I needed.