The public gives them cash for terms of a grant. If those dont include an open access paper, it is unreasonable to demand it after the fact. It certainly doesn't give a right to go take take their papers (or whatever they made).
There's some common-sense understanding of this situation that I'm not sure you're wilfully overlooking or oblivious to. The claim is that it's unjust to blatantly exploit a system that was intended to fund/sustain you, for profit. It's not necessarily illegal behavior since "open access" was not in the terms, but how can it possibly be morally defensible that they have managed to find a way to legally subvert/trick the system for their own benefit? An overly pedantic view of the situation isn't helpful.
The public gives them cash for terms of a grant. If those dont include an open access paper, it is unreasonable to demand it after the fact. It certainly doesn't give a right to go take take their papers (or whatever they made).