Kagan MacTane (he/him)I've been writing using em dashes since the 1990s. The reason AI uses em dashes is because it was trained on my writing, and that of countless other humans like me.
Janeishly@kagan Someone Swedish started writing to me (in English) about ten days ago using em dashes. I immediately asked if they were using genAI, because it's very rare for Swedes (or indeed anyone in Europe) to use unspaced dashes. They insist not, but still every message is florid, repetitive - and jammed full of em dashes. I smell an AI rat.
Michael Gisiger 
@Janeishly @kagan That is not true. European here, Switzerland. I learned the correct usage of hyphens, en- and em-dashes in my English classes at school.
German typography also uses hyphens (Viertelgeviertstrich) and en-dashes (Halbgeviertstrich). Em-dashes (Geviertstrich) aren't used that much anymore, but they should be used for lists (which are called Spiegelstrichlisten).
@gisiger @kagan Oh, of course some people did learn it, but it's most unusual to see anyone using them in casual chat. Even a lot of translators (usually extremely fussy about such things) often only use hyphens where they mean en dashes. And this was ostensibly someone who learned English in the UK, but who was using American spellings and em dashes. (There were other things that made me go "Hm", but these were the main ones.)
@Janeishly @gisiger I use them in casual chat... but I'll happily cop to being "unusual".