Good point. Maybe those races actually were there in FFT, just they were completely uninvolved with the 'human story' and kept to themselves, perhaps in a more primitive state of existence?

I mean, take the Macalania Forest spirits from FFX-2. They're scarcely noticeable in X, there's barely a hint at what they really are; but come X-2, and they've got number of sub-plots going on around them. Times change, and people(s) change with them.