Is it? I don't think most of the content LLM are trained on is written in the first person. Wikipedia / news articles / other information articles don't aren't written in the first person. Most novels, or at least a substantial portion of it are not written in the first person.

LLM write in the first person because they have been specifically been finetuned for a chat task, it's not a fundamental feature of language models that would have to be specifically disallowed