The law already is what it needs to be. JSTOR has limited access— and continues to do so through their terms of services— access to even old documents which are already lawfully in the public domain.
Their digitization is largely done by a for-profit company. It's not competitively bid. There are many parties who would digitize these works at no cost— archive.org and google for example, and could afford to do it without pay walling the results.
I was unaware of this. What company does the digitization for them?
Anyone at all (including you) is free to scan journals that are in the public domain and publish them online for free. If you scan/ocr them then there are many places (including Project Gutenberg and archive.org) who will host them for you.
Some contributors to JSTOR also make their articles freely available online. Many do not. Either way, it's not for JSTOR to decide.