Why would anyone want to move to another functionally similar microblogging site if Twitter still has more users?

Perhaps because the quality of the experience is better, even if the number of users is lower. As Twitter appeals more and more to the far right, those might not be the users people want to be hanging around with.

or specific forums like HardOCP/Forum screwing the pooch

ah genmay, that takes me way back

Nothing really replaced LiveJournal. Nothing really replaced Tumblr. SmugMug, Flickr, Blogger were all functionally similar sites that just never got as far. I think we’re going to see a bigger change in the style of the next social media site that reaches popularity more than we are going to see a functionally similar one replace Reddit and reach the same userlevels.

And I think we have the exact same problem with Twitter. Why would anyone want to move to another functionally similar microblogging site if Twitter still has more users? The problem we’re seeing with post, mewe, etc… General people don’t want to split themselves between several sites to keep in touch with everyone they know.

I feel like the Livejournal crowd settled into Tumblr and AO3, and the same people have accounts on both and their online presence intermingled enough you'd recognise a tumblr user on AO3 and vice versa. I feel like forums had yet to make the transition to something like AO3 for fanworks; the creators of the work (user generated data) collectively control their data. AO3 is now collecting and archiving scattered archives and restoring them or planning to restore them; the work is enormous and it is run by volunteers after all. The true legacy of Livejournal users are AO3.

If a forum site can exist where people can have absolute faith in the site like that, people will come. If a true non-profit forum can exist, maybe archives of dead forums can be revived.

But first, there must be the first call and there must be an answer. It was a massive work.

I don't think lemmy or the fediverse is the answer, not yet. On the other side Meta will undoubtedly dilute the fediverse, unless as strong an entity as the non-profit running AO3 can stand up. A collective body have to exist if only to shelter one massive instance, an instance that welcomes any and all so that the rest too can exist.