You can't determine what knowledge will be useful or valuable to someone in the future. Archaeologists have poured over receipts and shopping lists from ancient Egypt that were thrown away. It's why the Internet Archive backs up all the random webpages they do. There's no justification for mass destruction of books, especially since it's being done to train broadly useless LLMs.

Of course they won't be releasing these books later on. These companies want to hoard this text data so their competitors can't access it. It would also be illegally distributing copyrighted work. Aside from destructive scanning being faster, the fact that a book is destroyed makes the digital copy "transformative" and therefore legal if it isn't further copied or distributed. A judge ruled on this recently. I don't mean to advocate for copyright enforcement, but that's the reality here.

I think China has a national repository of AI training data that companies can access if they contribute to it as well. Doing the same thing in the West would at least blunt some of the harm the AI craze is causing, but that would have made too much sense.