Yea, for whatever reason, lemmy.world became the sort of de facto "main" instance, which isn't a bad thing and lemmy.world isn't a bad choice at all, ruud AFAICT is a dedicated and experienced fediverse admin.

There may be issues to centralising the user load too much. I don't have the technical knowledge to back this up, but it probably makes sense that there is such a thing as too much for one server to handle. If it has to handle all of the user requests as well has syncing all of the large and popular communities that a "main" instance is likely to host, then it's just a lot and probably requires technical solutions and investment beyond what one admin/team is willing or capable of doing. Plus, lemmy the software may not be designed for that sort of load, which probably requires a distinct architecture from that of a smaller instance.

So it probably, at point at least, makes sense to spread the load of both the users and the communities. However, it seems that redditors as accustomed to a "central" and singular service as they are have kind of opted in to re-creating a central "main" instance like they're used to. It may very well be a bad habit, as it presumes that there's just some giant server and a dedicated tech team sitting there waiting to scale up at a moment's notice. Of course, lemmy.world are free to halt sign ups and encourage users to pick other instances. But it remains to be seen how lemmy, its software and the fediverse/threadiverse in general handles communities/groups/magazines at this new scale.

In the mean time, intentionally spreading the load might help. As would donating to the developers and your admin!!