Yes, companies training LLMs would not let this degradation of quality happen. But that's not the question this point is answering. It's an answer to the though

Yes, companies training LLMs would not let this degradation of quality happen. But that's not the question this point is answering. It's an answer to the thought experiment of why LLMs won't be able to just become smarter and smarter by talking to themselves. The theory is that there is some point past which that will make them dumber rather than smarter, so it won't be done. We don't know for sure yet, but I personally find this theory compelling.