Reddit doesn't have to: phones do. Just long-press the hyphen key and you get a popover to select an em dash, en dash or bullet.

It works the same way on a Mac (key repeat off) or by pressing option+shift+hyphen (key repeat on).

Long ago on Windows I learned alt+0150 on the numpad.

Yet now my hard-earned attention to detail attracts nothing but false accusations...

Ain't no one got the time for that. How do you even know these things without looking them up?

If you like and use em dashes, you figure it out

I do. The point is that most people won't think about it, which is what we're talking about... There being a few outliers on a site called Hacker News who know the shortcuts for extended typography isn't in any way indicative of em dashes being in common use amongst phone users.

You spend a lot of time and money to study the humanities and have your work graded and corrected by picky professors.

Sure, but most people aren't humanities students. I feel the topic of conversation gets a bit lost in this thread at times.

I could swear I recently used a markdown-like input that would convert three hyphen-minus into an emdash. Jira?

Yeah, I remember Word doing that, and I manually did it when writing things like my honours thesis (which I typeset in LaTeX) or when I was writing HTML where the – and — would be liberally used.

But nothing I type in a web form would have them.

Are you sure it inserts an em-dash? Libreoffice will insert an en-dash, but not an em-dash.