" ...  Already there are driverless diggers and loaders,.."

As usual written by a STEM ignorant perpetrator of media content.
These machines are not "driverless" but remotely operated from above ground ! The driver sits in a comfortable control station and doesn't need to worry about tons of rock falling on his head  .-)  Such R&D projects have been ongoing for decades.

As in many dangerous, extreme  or combat environmnets taking care of the human operator imposes a significant mission overhead cost. Military drones, remote controlled vehicles ... are effective because the direct risk to the operator is eliminated. They are also now able to exercise extreme optimization of the function without regard to human limitations.