In my opinion, as Toriyama said, they're just Call of Dutying the licence. Either way you put it, one Final Fantasy a year (a year and a half precisely), even sold at 2.5 or 3 millions is much more lucrative than one big Final Fantasy every four years costing 100 million dollars. Plus, with this Final Fantasy XIII saga, Square can save money on the artistic direction, the conception of the world, etc. In short on every aspect of the previous games that are reused in the next.