That's some level of incompetence - the trappers I mean. A half arsed solution because they couldn't think of a better one. A registration system with abstracts and unlock-this-article links would be a better one, off the top of my head.
I'm willing to bet that they provide site licenses, where everyone in an entire university's subnet range might have access. In an open access journal, it shouldn't matter, but many journals are hosted on the same few platforms, and the spider trap is a feature of the platform.
