It's LLM-allergies.
The best fully-human writers of the next generation will be those who are very conscientious at grammar class and master all the rules, because by breaking them, they'll be able to push their prose to the most remote and unlikely locales in the geodesics of LLM-next-token-prediction-probability space. Such places where the Machines deign not trudge.
I'd argue that human prose can still exceed that of LLMs in clarity and simplicity.
This will always be appreciated regardless of any stylistic shibboleths indicating human authorship.