Surely this is an absurd exaggeration. I've been using em dashes everywhere (online comments, email, chat) for ~25 years now. I'm not unusual in this regard; everyone who cares about punctuation probably uses them liberally. They're not hard to type; on macOS you can hold down Alt and Shift while hitting the `-`, and on Android you can long press on the `-`. Maybe they're used less by Windows users?

Even just looking at my HN comments, 381 of my ~1200 HN comments so far (so >30%) have em dashes. This includes my very first comment on HN from 2009 (https://news.ycombinator.com/item?id=602094) and several that have multiple em dashes in them:

https://news.ycombinator.com/item?id=15169281 https://news.ycombinator.com/item?id=15899499 https://news.ycombinator.com/item?id=16596894 https://news.ycombinator.com/item?id=17291032 https://news.ycombinator.com/item?id=17464621 https://news.ycombinator.com/item?id=18201613 https://news.ycombinator.com/item?id=18331591 https://news.ycombinator.com/item?id=18387981 https://news.ycombinator.com/item?id=18843521

(and so on; all these are from 2019 or earlier, preceding GPT-3.)