In LaTeX (and probably smartypants which is another of those bare pre-unicode ASCII to fancy text converters that can get stacked into markdown--but I can't remember if dash handling specifically is in there), "--" is en-dash and "---" is em-dash. The single "-" gives a hypen which is handled differently than an en-dash in typesetting.
So... that's just to say that people who are exposed to the sorts of can't-unsee-it-now typesetting OCD that LaTeX and various popular extension packages within that ecosystem exposes can learn to write write "--" as en-dash.
It's sort of like being unable to return to the blissful state of not being hyperaware that Ariel and Helvetica are different.
It took centuries for the written word to acquire spaces between words, and then the US decided to jam them back together again.
Curious why folk are using two hyphens "--" instead of en-dash.