It was primarily the exhaustion of experts at tireless waves of newbies who hadn’t studied the available materials.

IRC being async if the client is run locally, modem delays made no difference (just as with QWKmail and forum posts). And for remote host IRC, I don’t remember what the IRC line length limit was but at 300bps you could get an entire message and the buffer scroll updates accompanying it in 1 second, which was well-sufficient enough to support peak volume with no relevant latency. And, I can still type a paragraph at clock seconds of input latency and remember where I’m at when backspacing. So, I would definitely not ascribe a desire for brevity as an outcome of modems.