let me give you a comparison of srb2 to kart, and compare why they work entirely differently when potentially optimized for mobile devices for the heck of it:
srb2 is a "hold forward and jump" kind of game. maybe there's some camera movement somewhere along the way, maybe a press of the spin or custom buttons, but there's nothing beyond that kind of complexity. holding down multiple buttons is a niche case scenario, and only really really applies when you're using an addon, which granted, is quite a lot. the only required keys for maingame gameplay, aside from enter, escape, WASD and arrow keys, are the spin and jump buttons. simple and to the point just like most sonic games are.
srb2kart is a "hold multiple buttons at the same time" kind of game. you're required to hold the acceleration/brake key to move at all times, and taking turns tightly requires you to hold an extra key in and of itself. in srb2kart, at the minimum there are five mandatory keys needed to play the game, even if you happen to leave out things like enter, escape or the arrow keys needed to confirm, go back/pause and steer respectively. these keys are also used variably throughout gameplay, with some keys needing to be pressed anywhere from almost never to at a moment's notice.
even if, theoretically, the future porters could implement auto-acceleration and gyro-steering, that's still four more buttons to take care of.
basically, the problem with an android srb2kart port isn't that it isn't possible or even doable, not by a long shot.
it's that it wouldn't be as fun to play as the native pc versions. at all. whatsoever.