There were of course many many reasons we separated the continents into their own worlds. Chief among them was that in "The Before Time", the stronkest power of the time had total control over the entire world and nobody anywhere could grow/expand/etc without their effective consent. This caused a lot of problems and forced a lot of people off the server. We've said many times before that allowing there to be three avenues of success that were mostly isolated was a very intentional decision and it lets people grow in a theoretical sense. We've talked about this at length before though.
All that said, the other reason we intentionally instanced the worlds was because we thought there was good chance we'd want to consider instancing the continents into their own servers. As we know, Minecraft doesn't "run well with lots of players" and because of that, we wanted to allow ourselves the possibility of a server-per-continent approach if we ever began to really really grow. Obviously Loka isn't high-population right now, or has ever been very very high pop. However, all the work currently underway is one of the last sets of feature-work we have slated before we started to really agressively start to advertise Loka again. Quests and some updated builds (that were blocked by 1.14 being poop) were the last big things we wanted in-place before we hit hard at YouTubing and whatnot.
Additionally, having continents/isles be their own worlds opens up the potential for being multithreaded (unlikely in any near-term). There are basically a number of performance concerns that we would potentially lose out on if we merged all worlds into one.
