One reason why LLM generated text bothers me is because there's no conscious, coherent mind behind it. There's no communicative intent because language models are inherently incapable of it. When I read a blog post, I subconsciously create a mental model of the author, deduce what kind of common ground we might have and use this understanding to interpret the text. When I learn that an LLM generated a text I've read, that mental model shatters and I feel like I was lied to. It was just a machine pretending to be a human, and my time and attention could've been used to read something written by a living being.
I read blogs to learn about the thoughts of other humans. If I wanted to know what an LLM thought about the state of vibe coding, I could just ask one at any time.