Wikipedia says
The 1969 edition of the Chicago Manual of Style used em spaces
between sentences in its text;[47] by the 2003 edition it had changed
to single sentence spacing for both manuscript and print.
Sentence spacing - Wikipedia
(“em space” is a double space)
so, fuck it, i guess. after i left school, the world decided to pretend traditional spacing didn’t make reading easier. whatever. i withdraw my suggestion.
EDIT: i think the key here is that the split screen allows us to see the formatted post. Antinous and I and everyone else was blissfully ignorant that the double-spaces we were composing were stripped out of the post until we could actually see it side-by-side.