FYI, there's also https://startrek.website/c/startrek. Several Star Trek subreddits combined to make it.
DamnCatOnMyDesk
It's not just limited to Lemmy and kbin. Technically any Fediverse-compatible site can interact with them (ie. Mastodon, Pixelfed, Calckey, etc). It's just nicest to do it from Lemmy or kbin because they are the most Reddit-like.
Think of them like email providers. If you have a gmail account you can send messages to yahoomail users without having a yahoomail account, even though they are wildly different email services. Same concept for all the lemmy and kbin servers.
Because we're in a period of rapid user migration and not everyone is aware of what communities already exist, or have a different idea about how they should be structured. After a couple months of people shifting between servers everyone will get settled and we'll see which communities will survive vs which ones will be determined to be redundant.
Well I'd argue Zelensky choosing to stay and fight did that. If he'd fled the country then things might have turned out very differently.