Android does not support certain options that a PC ren'py offers (alpha masked clickables for example, which is typically most of the clickables that aren't pure text buttons) so an actually playable android version may require at least partial rewriting of the game itself, including replacing some art assets. A ren'py game that's meant to run on android basically has to be written from the ground up with the constraints of android constraints in mind, which can affect visual quality (In game menus for clicking on locations looking very derp) or the entire game can be very, very basic in its technical design so these constraints never come up, i.e. a straight up VN without bells and whistles.