196 came into being on reddit long ago, and that is a cute (imo) holdover from then. The original community (195 I think) had 1 rule, post before you leave, and a second "rule", include "rule" in the title as a reference to the 1 rule.
It's not actually enforced of course, but it's part of the 196 culture
Someone probably liked the idea of it when they wrote it down, and then other people participated and I guess they also liked it.
I'm gonna argue that if the question was "why do people drink soft drinks?", an answer like "because they taste good" is more accurate than "because they're full of sugar which interact with the sweet taste receptors (T1R2/T1R3)"
If you want the latter to be more accurate than the former you'd have to get into a whole bunch of complications like how people respond to hundreds if not thousands of volatile organic compounds, you'd have to get into how sometimes a little bit of the purest form of sulphuric farty rotten smells inexplicably makes people say things taste better, and at a certain point you're asking for a full scientific paper on the niche subject which still probably won't satisfy so there will need to be more work, more papers, a meta study of everything, and then finally you have a video by Hank Green's employees trying to condense it down into something a lemming can misinterpret in a 60 word reply to you, "explaining" why the 196 community likes titles with "rule" in them.
You're like a dentist at a LAN party. We won't be able to justify our decisions to you. We'll just keep chugging monster cans and you'll either come to terms with that, or you won't.
Calm the fuck down. I think it was pretty obvious that the answer I was given, "because we did on reddit", wasn't satisfying. Nothing to overthink here.