Sales for FF titles (and JRPGs in general) have been on a downward trend since FF7, and they are getting more expensive to make. Logically the profit and cost lines will come very close to intersecting at some point in the foreseeable future. At some point they are going to have to do something drastic to a) increase sales, or b) decrease production cost, or c) fold the series.

It sounds unfortunately fatalistic, but the multi-platform release of FF13 and all the content supposedly cut from the game could be a interpreted as 2/3 indicators of the games no longer meeting an acceptable Return on Investment.