Not every android user has a controller or keyboard that can connect to it, why would you assume that?
Honestly, unless many people have been chiming in saying they have played it with bougie android peripherals, it seems like too narrow a niche to be worth it. : /
For what it's worth, I have played a couple FPS's made for android with touchscreen controls, so it's not impossible. ...Still prolly not worth the time to try and port an existing game that way, since it'd affect how much of the screen could be visible, but generally speaking, it's a real concept.
NGL, the concept of getting a special keyboard or controller to hook up to an android is bizarre to me. If you have money for silly peripherals, you probably have a decent computer you could hook that shit up to and play games on a proper-sized screen for them.