You're not wrong. There needs to be slightly better/more informative marketing that your communities are accessible from anywhere, and locale of the server doesn't matter.
People are joining lemmy.world before they learn/understand they can access communities from any federated node (which is nearly everything except beehaw)
It doesn't help that most instances are named/marketed as being for a specific subset of people. Like French, Canadian, LGBTQ, NSFW, US midwest, etc etc. Lemmy.world is generic enough to appeal to most new users.
you have Lemmy saying, "join anywhere!", but then all the instances are like "only join here if you are X, Y, or Z!". It is understandably confusing for new people.
But only in the early stage. If you got it once, it‘s like cycling a bike.
Best to understand ist to create another account on another instance and then subscribe the same community there. Then you can check which posts and comments are shown how on the feed
Federation seems to have its issues though, unfortunately. I created a post on lemmy.world earlier today (in hardware@lemmy.ml), and it took about 15 minutes for it to show up on lemmy.ml and sopuli.xyz.
If we consider something that is breaking news, 15 minutes is WAY too slow; there will be tons of duplicates posted from dozens of instances, even if they are posting to the exact same community.
That's most likely happening because of the over-centralization. If your origin server had been smaller federation to/from it and !hardware@lemmy.ml would have been significantly faster. Having a no-nonsense "urgent news" lemmy instance act as a hub for faster federation would be a great value-add for the community as a whole.
At some point I'll probably spin up a self-hosted instance, and rebase my operations there. In the meantime the fediverse needs content and users to reach a critical mass.
Over time I expect instances will grow and segment into more focused, specialized instances. Federation will keep things accessible so you might not need to follow. Communities of interest will grow around the instances that best reflect the spirit of that community.
Some splits will be amicable, some acrimonious, some out of necessity, others out if principle. Most will probably be because that's just where the content ends up.
Give it time. Nobody knows how this is all gonna work at scale, but at least we're doing it.