It doesn't look like the academics who are protesting the matter misunderstand. They realize full well that they are the ones that bear the sunk cost. They're the ones --along with the universities that employ them, and in turn, the taxpayers who underwrite the universities-- who spent years of time and money to reach a level of competence that would permit them to produce and referee journal-quality work. And many still persist in volunteering their time even after that, such as Greg Martin here. They often even transfer copyright of their work over to the journal. This seems quite different from movie studios that are sure to charge quite the fee for access to their hard-earned experience and works, and sure as hell won't transfer copyright to theaters and movie stores once the work is complete.
What major sunk cost is the publisher carrying, directly or otherwise? Digital distribution? That's not a zero dollar cost, but it doesn't cost hundreds of millions of dollars either, even if they can find someone who'll quote such a price.