Nothing to do with face buttons.

The analog stick gives way greater control over positioning than the digital key inputs of a keyboard. You cant move at half walking speed on keyboard but you can with a controller, for example. You also get more than only the 8 cardinal directions of movement. If you want to move at a 133 degree angle from your current position, you can do that with the control stick on a controller, but on a keyboard you will have to move your camera slightly to compensate. That's two actions on a keyboard that you can achieve in one action on a controller.