I attribute it to the fact that they have enough money to keep it up being as big as they are. If Blizzard's WoW 2 failed, they would be a-ok financially and have enough diehards to keep the game revamped just like it is now. If it was any independent company or smaller one i doubt this would happen.

Also its an FF title.

But there might be other reasons, just thats the only one I can think of realistically...