The thing is, in lots of contexts you cant easily type em dashes.

Google docs will convert “—-“ to an emdash but simple text inputs wont.

So when you see one in that context you have to consider the explanation. They copy pasted an em dash specifically, they drafted in Google docs, they know the unicode keyboard shortcut, etc. None of these are safe assumptions. And if it’s markdown you know it wasnt drafted in Google docs.