This started years before LLMs, as a way of signaling unconventional thinking. Maybe influenced by the UX of instant messaging.

That's my general understanding too. More recently people have adopted it as a way to not look like Ai, I've had several cite that as their rationale. There has been a notable uptick since the Ai step function change at the end of last year, along with all the other patterns we see, such as the one that underlies this new HN rule.