JSTOR doesn't lock content away. They make deals with existing journals to take content that is not available online and make it available online. Any access restrictions JSTOR imposes come from the content owners, not JSTOR.
JSTOR has also convinced most of these journals, even ones with restrictive access policies, to let JSTOR make their content available for free to the public at many libraries and schools, including ones that do not have subscriptions to the underlying journals. Because of JSTOR, many second tier colleges, community colleges, and even high schools have free access to vast journal libraries that they would not have otherwise had access to. They also do a lot to bring cheap or free access to vast journal libraries to schools and libraries in developing countries.
JSTOR has probably expanded free public access to scientific research more than any other group or organization.
Sure, it would be nice if everything were open access so you could just legally get it all on the net for free, but many journals aren't willing to do that yet, and in the meantime JSTOR provides a way for most of the public to get that content at the cost of having to visit a library or school that offers public JSTOR.
I can't imagine a way that's even figuratively true. The crime of burglary is about being somewhere that you're not supposed to; perhaps you meant to say it's like larceny of the public. But even then, it's a very tenuous connection you're trying to draw.
These companies were not taking anything away from the public; they made the effort to digitize, process, and catalog documents, which is no small task. And they set up servers to host these documents and make them searchable. If you feel they're asking too much money for these efforts, you're welcome to simply pretend they don't exist, and replicate their work yourself. They did nothing to make that task harder.
Now, if the companies destroyed the original public records or otherwise placed new locks around them that hadn't existed beforehand, then yes, your metaphor, while still hand-wavy, would at least hold water. But of course nothing like that actually happened here.
The "them" in the sentence you quoted refers to "the original public records".
The locks you refer to were around the new, value-added work: the digitized, processed, cataloged version of the papers they had made by adding value to the original public-domain documents. The locks were not applied to the original documents.
It's like the difference between storing a touched-up version you made of an Apollo 11 photo in a vault, and stealing the original photo negative from NASA and putting that in a vault.
JSTOR doesn't claim that its documents are public-domain:
Our licenses from publishers are non-exclusive, meaning that the publishers are free to license their content to others to digitize or make it available in any way they might wish. [0]
Not only were many of the papers in JSTOR funded by the public, but JSTOR itself claims to be funded through by the public through universities:
We do this with funds provided by thousands of libraries and institutions, all of whom are our partners in disseminating access around the globe. [0]
JSTOR cannot magically put documents in the public domain. It needs the permission of the original publishers. JSTOR is responsible for scanning a whole ton of old journals which would otherwise only be available as physical copies in libraries. Nothing JSTOR has ever done has ever made anything less accessible than it was before.
And locking away scientific papers of research that was funded with public money behind paywalls is burglary of the public.