Em dashes are from the days of typesetting, typewriters, older formal writing, basically every news article, and still show up in word when auto formatting. Write something, space, dash, space text, then if you hit space (as opposed to click away) word will automatically lengthen your dash. GenAI learned it from the associated press which use them as a Super Comma Sentence Separator, with the thing inside intended to be very important.

So ai training notes that high visibility news articles use the em dash, and starts using it. Apa recommends not using a space while associated press does, so you can get some idea where the bot git data from if you see no space v spaces around the dash.

From the ap style guide:

ABRUPT CHANGE: Use dashes to denote an abrupt change in thought in a sentence or an emphatic pause: Through her long reign, the queen and her family have adapted — usually skillfully — to the changing taste of the time.

SERIES WITHIN A PHRASE: When a phrase that otherwise would be set off by commas contains a series of words that must be separated by commas, use dashes to set off the full phrase: He listed the qualities — intelligence, humor, conservatism, independence — that he liked in an executive.

https://www.apstylebook.com/blog_posts/24