RIF specifically directed me here. I didn't join one before that because I didn't know which one was "best". I honestly don't care which one I joined, I just wanted to be on the one everyone else is on. I know this mindset somewhat defeats part is the purpose of the federated communities. I don't care about that in the slightest I just want a clone of Reddit.
Also "world" sounds more generic/standard than ml. Most people probably think it's a military website or something.
You'll probably find 90%+ of casuals are in the same boat as me.
Same, though ML made me think "Machine Learning", and that it was a more tech-focused place. This was before I realised they they're all (broadly) the same, and assumed that they were groupings of similar topics like an old web-ring.