World was already the biggest by far when I first started lurking back in July, and it's just getting more dominant. Before, there was quite some diversity in the distribution of generic communities, but nowadays the vast majority of posts that reach the top are from over there.
I really can't see any specific virtue that it has; uptime is not the best (or so I've heard), the moderation is quite lacking (which is demonstrated by the fact that Beehaw defederated them), they make some unpopular moderation choices (like blocking !piracy@lemmy.dbzer0.com), and overall the atmosphere is a lot less... nice than those of smaller instances.
I also feel like it goes against the idea of the Fediverse that one instance has control over most of the platform. Especially on Lemmy, where communities mean that building community within an instance makes so much more sense than elsewhere, and upvotes are federated near perfectly regardless the size of your instance, decentralisation makes a lot of sense. It really just doesn't make sense to me that Lemmy World is where people are going.
For the same reason cities form: the larger they get the more benefit there is to being there, so they keep getting larger.
I like the federation model and have switched from twitter/reddit to mastodon/lemmy. Still, we should expect and plan for massive instances, because of their inherent advantages. (More users = more content, more referrals to new users. Lower cost per user in terms of servers/resources)
Ultimately what I'd like to see are democratically run instances. Right now each server is essentially a benevolent dictatorship, which is fine when they're small and/or you don't have much invested in an account. Once they start to get big and making a change is a lot of work, it becomes more problematic.
Social.coop on mastodon is cool, however not necessarily geared to scale. I think if there was a multi-stakeholder coop where employees can make a living and users get input on how it's run, that could really take off.
I guess that is what people coming from corporate social media believe, but federation means that anyone, regardless the size of the instance, can interact with anything. When I switched from lemm.ee to Mander, which is a lot smaller, my user experience barely changed aside from that I can now browse science communities with 'local'.
e: grammar
That means nothing to the average Joe. Joe saw a comment mentioning Lemmy under a post on reddit. Got curious, went to join-lemmy.org.
"What the fuck is an instance? - he thinks. I don't care, where are the posts? Okay, a lot of these things seem to be specific domains, maybe they are for specific countries or interests. I don't have any of that. The fuck is federation? I don't fucking care, show me the posts already. Okay, .world is the largest, the name implies it's for everybody. Cool, register. Next, next, fucking finally here are the posts."
That's why.
But that doesn't make a lot of sense since it doesn't matter on what instance a community is hosted or a user first registered. That's the whole point of the Fediverse...
It makes a difference for the person hosting an instance. Suppose you're hosting an instance with ten users, and you run into some kind of configuration issue, and stuff isn't working right. Or maybe the server cost is more than you expected. You might just decide to let it shut down. If you have ten thousand users you might decide to stick it out because people are counting on you. Or you're getting donations from a hundred people, so you decide to make it work because so many people are counting on you, or maybe there's a specialist who's also a user, and they help you figure out the issue.