I'd imagine a good part of it is that keyboard + Mouse is not exactly relaxing. Its easier to take a keyboard on to a couch and play a game on a bigger screen if you don't need to worry about using a mouse for essential needs. 1 central device for controlling > two separate devices for controlling any day of the week, I like playing on my big screen and hate needing constantly lean forward just to play a game because of the mouse

. Although having said that my preferred controller setting is through gamepad and even in a game like FFXI (and likely FFXIV when its all done) you will still need to use a keyboard of some kind if nothing but to write new macros and chatting.