I have a feeling it was the standard because they used the minimum font size to make the letters readable, and that's how much it fit on the physical page width. Which was standardized before typewriters for unknown historical reasons?
> You don't want to move your neck when you read a single line that's kinda silly.
I don't have to move my neck to read the article spread across the full width of my monitor. On 13" laptop or 24" desktops. Are you using a 21:9 utrawide?