When human beings write we do so with a particular perspective with an intention to communicate to a particular audience. Even the driest scientific writing is partially informed by the experiences of the researchers, no matter how hard they try to remove it. Human writing has a viewpoint.
LLM generated text always lacks these elements. It's always some bland, shapeless sequence of words pulled from the ether. I'm sure with time and effort you could combat this and give LLM text more of a human feeling by giving the LLM enough context about your communication, but that would take work, which in many cases would defeat the purpose of using the LLM instead of doing the writing yourself. And if you care that much about your communication with others (and you should!) you'd probably just find using LLMs frustrating to begin with.
LLM generated text always lacks these elements. It's always some bland, shapeless sequence of words pulled from the ether. I'm sure with time and effort you could combat this and give LLM text more of a human feeling by giving the LLM enough context about your communication, but that would take work, which in many cases would defeat the purpose of using the LLM instead of doing the writing yourself. And if you care that much about your communication with others (and you should!) you'd probably just find using LLMs frustrating to begin with.