Most people default to the main server. It’s easier that way. A major weakness of Lemmy is how if I use the main URL of another instance, it will say I’m not logged in, and I have to cut and paste a parameter and paste it onto the end of Lemmy.world to gain access. It’s kind of annoying so since most of the main action is on Lemmy.world, I prefer to make an account here and stay within this instance as much as I can.
I see your point but there have been community-run message boards funded by donations in the past. I doubt Lemmy will replicate Reddit’s scale.