If there is a settled policy on open threads, maybe they should be created by a bot. But it seems to be working fine, in part because people can (and do) create one at the right time simply because they want to post in one.

But you are simultaneously suggesting a new meetup policy and automating it. If there is a need for a new policy, that's a pretty good reason not to automate it.

There used to be a system of posts with multiple meetups, much like passive fist describes. Those were simple reminders for well established meetups. New meetups do need advertising, both for new members and because they usually don't start with regular schedules. Added: this is stilling going on, run by Frank Adamek, so the proposal seems moot. Instead, the question is how to get people to work with Frank (if not continue their current system).