This is a complaint I hear others voice and one I have myself. I think it comes down to the text being poorly written. Sure, LLMs are good at a lot of the surface indicators of good writing: they have a wide vocabulary, they use grammatical sentences, they break up the text into paragraphs, sections, and lists. But they're terrible at organizing the text and marshalling a concept to get it across to a specific audience. The section and paragraph breaks are meaningless, the metaphors are unenlightening, the rhythm is exhaustingly uniform. Pre-LLM, you'd find this kind of text in marketing materials, corporate PR, and heavily padded sophomore essays.