Blame copyright law. AI training is very comparable to compiling an inverted index, which is considered transformational even though you can recover the input documents from an inverted index.
To be maximally charitable, while creating large language models has been ruled to be transformative and thus fair use under current copyright law, Anthropic did separately violate copyright law when procuring copyrighted text from LibGen and Pirate Library Mirror. That being said, I agree with you, creating LLMs from copyrighted material is very clearly not a violation of copyright under the current legal regime, so long as you procure the text legally, be that through web scraping or by purchasing books directly. And it’s annoying that people try to muddy the water on this.