Which hand position? You have flats, hoods and upright cruiser. In that pic, if it were me, I might have routed the cable under the bar and put the shifter a bit more outboard to allow resting the palm in the space where the three bars meet but that's just me.

I can't speak for others but it's a factor of cost and reliability. Thumbies work, can easily be worked on and are cheap. Those are some pretty big plusses in touring.