Why did Square do it?

[Rostum]

It's kinda like what they did with FFXII (getting a completely different team working on the game) only the team that worked on FFIX did the exact opposite of what would be done with FFXII in that FFIX does indeed incorporate elements of so many games while FFXII just has the spells and equipment.

Except, you know, FFXII was set in Ivalice so it has a lot of references to FFT and FFTA...