A number of comments are along the lines of "people will just pirate books from Library Genesis / Anna's Archive". It seems obvious the motivation is cutting off the supply of new books to those sites.
I don't see how their measures will help. It might have helped a few years ago, but one can literally ask to recreate the full book contents 1-to-1 with any local uncensored LLM just from a video of changing pages. You don't even need to break a DRM in a classical way.
If I were them, I would rather respect my users than fight with windmills.
That's putting a lot of trust in the LLM to avoid transcription errors, especially in books that include equations and similar complicated formatting, books in languages not well-represented in the LLM's training set, etc.
To say nothing of books with pictures.
As an alternative, why not hack the Android Kindle app to spit out bit-perfect DRM-free copies, with or without the assistance of the same LLM?
If I were them, I would rather respect my users than fight with windmills.