People—like me—who’ve used latex often learn to love en and em dashes. I think they are great, and I appreciate that people care about typography enough to use them. I also use an Oxford comma. It’s about care and quality; the fact that LLMs use them suggests that they are preferable. I’d encourage everyone to start.
My theory is that the models deliberately use em dashes and other tells to troll humans. The underlying message is, "watcha gonna do about it, meatbag?"