We consider the crossroads as a world, because there are some useful things you can learn from these Crossroads.
Summary
So, the Crossroads are the place beyond Kingdom Hearts, and before Castle Oblivion/Land of Departure. It's
a particular area that many people overlook. Even though it hasn't been officially released, we know that the grassy Crossroads
in Chain of Memories, is actually the same world as the Keyblade Graveyard of Birth By Sleep. Why? Well, with the
original Land of Departure nearby, and Kingdom Hearts nearby, it's assumed that it has something to do with the past plans.
Because, you see, the Land of Departure and the Keyblade Graveyard are very closely linked worlds. They
were both near each other, and both very similar. Now they are the crossroads and Castle Oblivion, which are somewhat linked.
Also, Master Xehanort was able to call Kingdom Hearts from the middle of the Keyblade Graveyard, and it
appeared in the sky. So, this shows that Kingdom Hearts is nearby, and used to be an actual moon. Of course with huge explosions,
and disappearances and such, Kingdom Hearts lost its shine, and disappeared, but was still roughly in the same area.
The Crossroads are more of a walkway between the various realms instead of taking Gummi Ship or Keyblade
Ride through them.
