[zozbot234]

My guess is that the "revenue streams" from reproductions of public domain content are (1) negligible to begin with, and (2) might even be higher for many institutions under a permissive policy, since paying for the institution's implied endorsement would still be a highly-sought-after signal for most serious commercial reusers. Many institutions are starting to realize this, even in Europe where these overblown copyright claims used to be even more common.

[tingletech]

I think this is true mostly, but not all cultural heritage institutions are on the same page here. I work on some sites that serve the cultural heritage community, and last time I talked to some of our larger contributors, reproduction rights were still a revenue stream that was large enough to want to maintain. For some contributors, it is not worth their time to try and deal with licensing.