I think the specific way that Lemmy/Kbin are growing is not exactly how the creators, particularly the Lemmy devs, envisioned it. I think they believed people of a specific interest or ideological leaning would band together on an instance, make a few communities that were relevant to them, and federation would allow their work to be shared and for them to venture out to participate in whatever they thought was neat. The best examples I can think of off the top of my head are probably Lemmygrad and the Star Trek instance that hosts three communities related to Star Trek (memes, general discussion, and deep-dive nerdery). I think the notion (I doubt it was a fully formed plan) was that instances would have relatively little overlap in the types of communities, and even less in the content.

How growth is actually happening is seems to be turning out fairly differently. Reddit is basically having these little spasms (or maybe just coughs at this point) where a few thousand people leave at once, and many of them are heading to L/K instances. Sometimes we don't quite fully understand federation when we arrive. Sometimes federation is down for a bit. People are basically flocking to established but previously tiny general instances with no particularly strong agenda, and seem to be creating communities with no particular concern about fragmentation.

This may not have been how federation was envisioned, but it creates its own kind of flexibility, where instead of X% of communities being at risk when an instance goes dark or goes crazy, it's Y% of content. I think giving users the option to adapt to this state of affairs by implementing something like persistent multireddits we could subscribe to or just a setting to "autocollate" identically named communities would be really helpful, eventually. In the meantime, trying to understand how we got here makes it easier to accept where we are, and hopefully lets me stay on the right side of the line between being a valued user and a pain in the ass, LOL.

Because they're different communities, and that would just be spamming a bunch of people you're not directly engaging in.

It's the mail flier version of community engagement.

Consider a community callled "politics" on lemmy.ca. Do you think they will want to be flooded by posts about American politics? UK politics? German politics?

No. Probably not.

They're a different community, made up of different people, and if you don't want to engage with that community in any real way, you should not thoughtlessly and automatically post things to it.

I could see it being taken advantage of, say I start a community on my instance called c/games, and crosspost a bunch of offensive content across all federated servers. But I'm still new to this and might misunderstand how it works.