I think you are right about the narrow legal distinction, although I was not suggesting that the public has a right to enter someone’s home and scan a book merely because its copyright has expired.
A privately owned physical book and the public-domain work embodied in it are different things. Keeping an old book in a dresser, even without providing access to it, is also meaningfully different from deliberately acquiring the sole remaining copy in order to extract its content, destroy the artifact, and preserve exclusive commercial control over the only remaining usable version.
Destroying the sole surviving copy would not literally steal publicly owned property. But it could irreversibly remove a public-domain work from practical human access and destroy a unique piece of cultural heritage.
In that very narrow situation, preservation, archival deposit, digitization, or public-access requirements may be justified, especially when the material is acquired for commercial use that depends on destroying or withholding the only surviving source.
The company would not be reasserting copyright in the legal sense. It would, however, be creating copyright-like control over practical access.
The work would remain legally free for everyone to reproduce, while the company’s conduct made it impossible for anyone else to obtain it.
I know there are more pressing issues than this one in the world, particularly those involving immediate human life.
But I also believe that the value we assign to human life is connected to the value we assign to human knowledge, memory, invention, and culture. When those things are casually treated as disposable inputs for extraction, something important erodes.
Companies should be free to use public-domain material commercially. The issue arises when that use creates a negative externality by permanently destroying the public’s future opportunity to access and use the work.
Mining our cultural heritage and locking away what remains is still extraction and exclusivity.