How about this: What if our Earth was simply another world in the KH multiverse? Remember, Gummi Ships are the only thing that can traverse the gap between worlds, and then only because the worlds were recently linked. Until that point, each world was completely seperate from the others. What if they aren't simply worlds, but perhaps entire seperate dimensions, and only the Gummi blocks (which came from the void between dimensions) can survive the interdimensional passage? Mayhap our world is connected, we simply haven't found the Gummi blocks needed to access and traverse the void..?