You have missed the obvious reason. They needed a button so you have an ability to lock the car without having to pull out the smartkey. if you had it touch or the switch inside the door mechanism, it would simplifiy the unlocking but make the locking part of the process that much harder. And put that along with the people who would want to cut a wire to remove any cirp sound you would be left not knowing if the last touch you had on the door handle locked or unlocked the car. or would you just go by the position of the side mirrors and hope that nobody inside flipped that switch that forces open or closed the mirrors.
2018 Niro EX - Ocean Blue
GTA - Canada.