I think alongside trying to foster more upbeat/constructive communities, it may also help to have a mixture of novel/different posts and if relevant, helpful posts.
The first is definitely niche, second is maybe somewhere between, and the last benefits from being widely appealing, but what they each have in common is that there’s something different to come across from their posts. First is satellite imagery, second courtesy of a couple posters is some weirder pocket knives, and the last is more or less like pics but with a bonus of being a variety of images you could use on your phone or PC.
A tricky part with each of these so far has been that despite some upvotes, you may not see posts from them too often depending on your sort setting as they don’t often draw too many comments to each post.