What happens if you are happily pottering along in autonomous fly mode when one of your passengers sneezes and lands a great big goob on the bottom left hand corner of the touch screen that controls the flight - right on the cancel button? Wiping the touch screen could put you in aerobatics mode. Would the flight still qualify for green credits?
Building your own hardware to a high standard is expensive. The actual up front costs of building something physical is not that much (look at Raspberry Pi) but the cost of certification to minimum safety standards and protection of intellectual property are quite high. It wasn't too long ago on this forum that someone was quoted north of $200K to replace a failed screen on their AW109.
When I think of all the dumb birds that have strayed into my flight path, or the vehicles/personnel that have strayed into my approach path, I know these things are just gimmicks.