oh, i see what you mean now

but wouldn't that still be the case if you were handwriting your newspaper and xeroxing it or something

where does the printing press come in

also though i don't think fine typography is mostly determined by newspapers

"Em and en refer to units of typographic measurement, not to the letters M and N. (Yes, the homophony is confusing. To disambiguate, loud print shops referred to them as mutton and nut.) In a traditional metal font, the em was the vertical distance from the top of a piece of type to the bottom. The en was half the size of the em. Originally, the width of the em and en dashes corresponded to these units."

https://practicaltypography.com/hyphens-and-dashes.html

Handwriting allows one to vary the point (width) of individual letters. Printing presses do not afford that luxury.

sure, but you can still leave horizontal space around your dashes—or not

what we nowadays call 'microtypography' and think ourselves very avant-garde for employing is ubiquitous in medieval illuminated manuscripts; every line is full of subtle variations in letterforms to better fit the available space