While it is difficult to play some types of games with touch controls the vast majority of people who own Android devices do not have gamepads for their devices. If you published a gamepad-only Android game you would not have as many downloads as a version with touch controls. Also, the nVidia Shield isn't very popular, so you probably wouldn't get very many downloads if you published for that, either. Modern Combat 5, a first-person shooter for Android that has touch controls, has over 100,000 downloads, and most people who have that game probably aren't using gamepads. This proves that people will buy an android shooter game, even if it has touch controls.
I hope that helped