I imagine the commenter is worried that if it's open source, publishers can read exactly how it works and then adjust their setups to defeat it. Vs I suspect publishers already know how it works, or could figure it out from their own server instrumentation, or by inspecting client code (I haven't looked at this project but I know a few I've seen previously work mostly with JS and CSS modifications).
Also it's one thing to shut one instance down.. entirely another to shut down a whole bunch (not to mention private instances)
Of course they know. I have seen local newspapers who managed to block archive.ph's mechanism. If a bigger outlet does not use technical measures against services like wallhop, it is safe to assume that’s deliberate.
It makes sense economically since the part of the population using such services is so small and may have specific demographics that justify specific treatment just from a marketing POV.
Then you want search engines to get the whole content (okay at least before they started to summarise everything but the kitchen sink) - that will always leave a loophole.