I'm pretty sure they've already consumed everything on Anna's Archive, The Pirate Bay etc., and they are now buying books to fill the gaps and to legally launder the corpus they already had. It has little to do with ethics (one could also question the ethics of buying rare, second-hand books and then destroying them).
I believe that is exactly what the parent post is doing
Because a cartoon mouse's parent company used regulatory capture to extend copyright for decades.
They're basically rebuilding Google books, and keeping it private. That's privatizing all of humanity's knowledge. Then from what I see some other missing books are just rephrasings of other books, which can already be done with synthetic data using another LLM to generate it. I would assume a lot of those books are school text books as well, which are almost never digitized and are rephrasings of university text books. Maybe they are not able to generate synthetic data of sufficient quality and are resorting to human books that rephrase information instead