Another commenter above this proposed a pretty compelling theory for the source of this style: SEO-inflated prose online. If the models were trained on the internet, "higher quality" content needed to be indicated to them during RL somehow. Search engine ranking is an easy-to-obtain metric that's kind of like "quality" if you squint, turn around, and lobotomize yourself. So the AIs have a high likelihood of producing the kinds of content that is rewarded by Google SEO.
Search engines only show a snippet of the content and that always looks convincing. It's the whole content that is off and, unfortunately, a few seconds/minutes can pass before you realize it (If you ever do).
Search engines track that. It's what a "long click" means. If you click a result, then return fairly fast and keep searching or clicking other links, they infer low quality (for that query at least).
Well, and Google's proxy read of "quality" might have flawed assumptions. A concise page where you get what you need and leave quickly might read as "high bounce rate".
