I wonder if this horizontal glyph direction has some sort of meaning lost to the sands of time. Armchair speculating outloud, maybe it’s not purely aesthetic and could imply some sort of past/future tense?
I don't think it does. Chinese, Japanese and Korean had been using vertical writing for centuries, only switching to horizontal ones around 20th century for interoperability with Western writing (such as math or chemical formulae).
Mongolian script, from the link presented here, has actually switched from being horizontal to being vertical (under influence of Chinese).
