Actually what is also needed is a notLLMs.txt. robots.txt exists, but is mainly for crawling and also not sure anyone follows it or even if they don't follow what's the punishment.
Some AI companies follow robots.txt (OpenAI and Google, for example) but others ignore it. There's also other limitations around using robots.txt to sole this problem: https://searchengineland.com/robots-txt-new-meta-tag-llm-ai-...