Quote Originally Posted by GLR
Or Square was just lazy.
Or maybe the extraordinaryily long FMV sequence at the end of the game just took up a lot of space on the fourth disc. And instead of cutting the ending short (which I'm so glad they didn't), they cut the cities. But since you have access to anyplace that doesn't have people in it (i.e. the Centra Ruins, the Deep Sea Research Lab, the Chocobo Sanctuary, ect), I'm going to have to go with what BigD said.