It's not as complicated as it seems. How I would explain it to reddit people:
Think about Reddit and let's say Digg. Imagine if you could use digg.com but also see posts from reddit on it. There would be an "all" feed with posts from both sites, each labelled as coming from either reddit.com or digg.com. There would also be a "local" feed with just the digg.com posts.
Now switch reddit and digg with lemmy.world, aussie.zone, and a hundred others.
Now switch reddit and digg with lemmy.world, aussie.zone, and a hundred others.
And that I think underscores the problem; most people want a social network, and not a hundred loosely connected social networks.
@threeduck@aussie.zone you're gonna be famous.