I thought the only rule was that you had to post, not anything about the title. Having rule in the title just became a stylized tradition, since it's the lowest effort title (besides "title") and the posters were forced to post something, even if it's low effort. Now users would probably downvote anything that doesn't have "rule" in the title somewhere but I dunno if mods would ban for it or not. would be pretty cringe tbh