> And if it was such a vital part of punctuation, it would have been on our typewriters and therefore on our modern keyboards.

Typewriters were monospaced, which gives you extremely limited scope for distinguishing hyphens and em dashes. Small wonder that they didn’t bother attempting a distinction, and then that provided the inertia for us to never get such a thing now.

Typewriters are a lowest-common-denominator sort of thing. They lacked all kinds of widely-used stuff, and some of it they killed by their omission. Accented letters you mostly couldn’t do at all, and the rest of the time could only do by a terrible hack.

There’s a similar story in the final death of the letter thorn (þ) in English <https://en.wikipedia.org/wiki/Thorn_(letter)#Middle_and_Earl...>: imported fonts lacked the character, so people substituted it with y which looked most similar, and that substitution became ubiquitous, and now most people think the first word in “Ye Olde Curiositie Shoppe” is pronounced /jiː/ (“ye”), whereas it was actually just how they spelled “the”, so it was /ðiː/.

It’s a general rule in such technologies: although they make many new things possible, they also damage what was there before.