Same. I feel like I've been using "--" in my online writing for decades now. Take that, LLMs; I used it before it was cool... er... before it was a weak signal that a piece of text was written by an LLM.
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.