Respectfully, who cares?

Hard truth... you're not important. None of us are. No one cares enough about your opinions that they need you to "maximize your reach" by posting in multiple places. That is entirely a you problem, not an us problem.

No one is forcing you to post everything multiple times to multiple communities. You're free to choose one and post to it. if it's interesting enough, someone will likely share it to other communities. And if it isn't interesting enough, they won't. Simple as that.

that's... how... it.... works

Also, you talk as though browsing r/all on Reddit doesn't also show multiple copies of the same post sent to multiple communities. Of course it does. Declaring something the "main" community isn't going to change that anyway.

Did I just read a complaint about cross-instance posting, that was cross-instance posted?

I think the mods of the duplicate communities should join forces, agree on uniting the communities and close all but one (the other pointing to the united one).

I don't think there's really a good reason to keep communities split. (there are of course contingencies where it makes sense, like rogue mods etc.)

people having to subscribe to both to see the content

Not a problem. Just subscribe to both. It's no big deal.

posters having to crosspost to both

Don't do this! The above "issue" already solves this. If I want to see posts from both communities, I'll subscribe to both communities. Posting the same content in both will cause me to see duplicates.

Let it be. The duplication problem is all over the Fediverse. Over time some of those communities will die out and some will become more distinctive or specialised, attracting specific engagement in their own right; the problem will solve itself.

That’s part of the fediverse. It will be a obstacle for communities that will keep them from getting Reddit sized but decentralized means they aren’t supposed to get too big. I think the best compromise would be allowing you to create multi-communities on the front end or in the client.

But end users may not want to federate with Lemmy.world or Lemmy.ml or overzealous moderators may ban a user on one instance and for that reason I’m not in favor of consolidating communities. I’d rather both grow organically

As someone else mentioned, this sounds like your FOMO on your reasoning. But more than that, having a single instance would actually hit less people ultimately. What happens if the combined community is on an instance that is defederated from others? The other people won't get or see the message. What would the alternative be? To force defederated instances to get combined communities? At that point you're breaking the underlying nature of the Fediverse.

I like having different communities on the same topic having completely different posts. Makes things feel less boring.

I think from the technical point of view, it should be possible for users to merge multiple communities into one. I think the git software could be a great template for achieving this. The admins of each community would only be responsible for their instance of the community. The same merging could apply to comments.

The big challenge however would be to automate this into a seemless experience for the user. If the goal is to attract more users, the user experience has to be on a tiktok level of simplicity.

An additional problem, where I don't have an answer yet is: What is supposed to happen if two communities start in the same way, but develop into different directions?

Edit: Seeing the new comments: I like the social approach of admins coming together and collaborating in a single community even more. But it would still be nice, if a community could be hosted on multiple instances at once, for redundancy.

To be fair, to some of us this is a feature not a bug.

A technology post on a technology/infosec/IT focused instance seems to have a COMPLETELY different focus and conversation than one on the larger instances, for example and I don't want those mixed in with people saying that AI is a Jewish conspiracy to take over the world.

There are smaller dedicated art focused instances popping up too. I'd expect that they're going to have a better set of conversations around those subjects than the same threads on a general instance and I don't want those mixed up.

If it's a subject I really want to see a lot of discussion about, I'll look at multiple threads... can this mean that some subjects won't have as good of a conversation because people aren't bouncing off of each other? Yeah, absolutely and that frankly SUCKS, but, as stated, it also means that some of the niche conversations have a chance to grow where they may have previously just been unseen due to how many people are talking.

To me, they're on different instances for a reason, let it grow organically. The ones that stand out will wind up being the main ones people use.

As for amount of users. A decent amount of those are likely alts people created when instances were having problems or just to try out the different locations.
Or, people just didn't like the Fediverse for all the reasons you stated, which is also possible, but I don't necessarily think chasing numbers should be the end all goal

It's unfortunate, but I doubt anything will be done about this. Guess we have to get used to seeing the same posts, and repeating ourselves in threads a lot.