Why is the majority of final fantasy 7 on disc 1?

Answer 1

Because it would be more hardship to half fill the first disc. It would be impossible to fit a file as large as this game onto a single disc. So after a disc is filled the remainder of the file will be put onto the next disc, then the next if required, and so on. So the latter part of the file will always be on the last disc. It's all down to the file size. It can't really be helped as to how much of the game goes onto which disc.