My understanding is that business shorthands were phonetic, so they were very useful for taking notes that would later be transcribed by the same person that took them, but much less useful for written communication between various dialects of the anglophony.

(did the period when shorthand was a school subject coincide with the former use of "eye dialect" by writers?)

ha, I learned shorthand in second grade (and yes, it was already an antique by then). I wonder what a multimodal language model would say to shorthand...