Skyrocketing development costs and disappointment with the PS3. In recent Gamespot interviews with the president of Sony Computer Entertainment France and Final Fantasy creator Hironobu Sakaguchi, these were the reasons given why Final Fantasy XIII may be heading to the Xbox 360.
If "the one RPG franchise to rule them all" should indeed happen to land on another console, it would be a huge blow to Sony who recently lost exclusivity rights to the Devil May Cry and Ace Combat series. Conversely, it would be a huge victory for Microsoft who's been desperate to woo Japanese gamers into buying the 360 since.
Source: GWN