I think OP is referring to the fact that bad actors, who are exploiting facets of SEO (rather then providing "meaningful" content), use to need to programically generate content (pre-AI/LLM).
For a real reader, it was obvious (at a quick glance) this was meaningless garbage. As they would often be large walls of text that didn't make sense, or just lists of random key words.
With LLM/AI, they're still walls of text and random key words, but now they grammatically/structurally correct and require no real effort to generate. Unfortunately, it means that the reader actually need to invest time in reading it. You'll also notice a growing trend in articles (especially in "compare X vs Y" type articles), the same content is recycled and rephrased to "pad" the article and give it a higher SEO ranking.