This has always seemed intuitively obvious to me. I use a lot of em dashes... because I read a lot. Including a lot of older, academic, or more formally written books. And the amount used in AI prose has never struck me as odd for the same reason. (Ditto for semi colons).

The truth is ... most people don't read much. So it's not too surprising they think it looks weird if all they read is posts on the internet, where the average writer has never even learned how to make one on the keyboard.

Delve on the other hand, that shit looks weird. That is waaay over-represented.