But the destruction is the essential part, ironically, that makes this copying kosher for copyright purposes:

Destroying books, it turns out, isn’t just cheaper than maintaining them: The presiding judge also ruled that it’s transformative enough to constitute fair use under Section 107 of the Copyright Act.

So, somehow, destroying the books afterwards makes it all legal. In spite of the fact that no author who wrote a book in all of human history before about 3 years ago had to worry about a chatbot sucking up all of its work, and vomiting it back out, without compensation.