That's not at all how it works. There aren't going to be 15 different mini forums, one for each instance. Only one instance needs to have one, and the rest can connect to it.
That just doesn't stop people from starting duplicates on other instances, same as on reddit, someone can start another sub for the same thing with a slightly different name.
I think you've misunderstood. Lemmy/Kbin absolutely DOES allow for one big forum to exists for a subject, across the whole fediverse.
It's just that people are creating communities on their own instances, because they don't know or care that one already exists on another somehwere, which they could be joining.
They are two separate communities. They are like if you had two subbreddits called r/startrek and r/alsostartrek.
They could be about the exact same thing, but they were started by different people. The second of which, either didn't check if one already existed, or wanted to make their own for one reason or another.
In the future, it might be possible to combine communities in some way (like multireddits), but for now, all they have in common is the subject matter.
And, while communities have a "home" instance they are not solely accessible by people on that instance. They are accessible by any user on any other federated instance. Making more communities for the same thing on other instances, is not how federation works. You're just making more "subbreddits" with similar names.
Basically, both communities exist on both instances. Only one is needed, on one instance, for there to be a community for a given subject on the entire fediverse.
You can view the Kbin magazine, of course: kbin.social/m/startrek
But you can also view the lemmy.ml community, still in Kbin: kbin.social/m/[email protected]
And the same works in reverse, the Kbin magazine, in lemmy: lemmy.ml/c/[email protected]
Basically, someone made a second one, even though only one is needed. They both exist for the entire fediverse, not just their respective instances.
Wont open from kbin.social. My other community works, tho. Weird.
I suspect he just straight up logged out and went off into the sunset...