There are countless other 'niche' communities that have no posts for months, however.

Hey, have you seen !fedigrow@lemmy.zip? It's got a lot of discussions on how to handle this.

I think that to grow a niche community, you need at least 2-3 regular posters, and you need to make posts that encourage discussion (i.e. ask questions or provoke a thoughtful reaction that readers would like to share.)