Isn't that up to the creators though. If world is their home instance, why would they create elsewhere? Not being able to create communities would kind of defeat the purpose.
If creators want engagement, they will create on subs with more uptime. That will likely be world in the future, when hardened. The ddos attacks aren't good for Lemmy now, but it should iron out some wrinkles in the long run for all instances. I think the world admins are doing a great job, both technically and communication wise.
I think you put too much stock into the ddos explanation. I'm not saying it's not a thing, but there are bigger issues that it seems won't be resolved before Lemmy 1.0
Regarding your first question, tf is my home but I have created communities on different instances. Some instances because the community fits the instance, some because I like the URL. I figure it's best to decentralise as much as possible.
As to your last point, I think some of what the admins at world have done is tremendous and I celebrate their commitment to world, but there's limitations to the software, as they well know and ultimately this is a decentralised platform of which loads of little instances are supposed to make up the larger whole.
I kind of expected some people to start instances for mostly just making accounts (some of which I have seen), and for other people to make instances just for community hosting and disallow account creation (and afaik this hasn't been done to any appreciable degree). I'm not sure this is even possible or functionally useful with the way lemmy currently works for community creation and stuff, so maybe that's why it didn't happen.
Honestly I even expected some instances to pop up with the sole intent and purpose of serving one community, but even stuff like the startrek instance have account creation available.
Maybe it's because lemmy is so new for people. Niche instances would rather host accounts than scare users away in an effort to get them to sign up elsewhere.
Well that would explain why there isn't a general use community only instance. Honestly that feels like a feature that should exist, while still leaving "local only" as an instance setting for people who like it that way.
Still seems odd for instances with a specific set of premade communities with new ones disabled to worry about hosting accounts, like the startrek one.