Who says they're rare and nonrecoverable? If they're bought in bulk from used booksellers, they're probably quite common titles. We throw away nearly a billion books every year. They're not sacred, and scanning a few million isn't a tragedy. People just don't like AI and want to be outraged about it.
And... at the very most... each AI company destroys ONE copy of a book.
But still, the number of duplicates will be inversely proportational to the rarity of the book. Lots of copies of James Patterson and Twilight, probably few or zero rare 16th-century manuscripts.