Because they're not really a safety issue in an aircraft. When you're in cruise flight, things happen slowly. Heck, on a pre-touchscreen general aviation GPS u

Because they're not really a safety issue in an aircraft. When you're in cruise flight, things happen slowly. Heck, on a pre-touchscreen general aviation GPS unit, you dial waypoints in one letter at a time with a single rotary knob. As annoying as the touchscreen is, it's still an improvement - and you still get your single rotary knob in case things are turbulent, so it's no really any worse. Takeoff/landing is a different story. Things happen quickly there. But you're also not messing with the avionics during those phases of flight. As the saying goes: aviate, navigate, communicate - in that order. Touchscreens are mostly the realm of navigation and (sometimes) communication.