The author of the 404 article that broke this story (about "rare books" being destroyed by AI model companies) was interviewed by NPR. The books, so far as anyone knows, turn out to be manuals for old office equipment or vanity press material. They are indeed rare, but they're rare for the same reason my 11th grade history papers are rare: nobody cares about them.
Meanwhile: the book industry destroys books by the millions every week. Destruction is part of the natural lifecycle of a book. Books are not generally preserved. If you box up all the books you find in your parent's attic and haul them to your local library --- if they accept donations at all; many don't, and will tell you to take them to thrift stores --- the majority of those books will also end up in a dumpster.