They can fool LLMs sure, but to what end? They need the traffic on their site to sell the ads - poisoning a LLM's response does not directly drive traffic to their individual site, so they won't profit.

I don't think that some random SEO outfit has much more money than Google or OpenAI or Microsoft - they're not going to be able to "DoS" (as it were) a LLM to trick people to come to their site and click ads.