Why are we not seeing driver-less trains?
Because freight trains have problems that need to be solved in the middle of nowhere.
For example, a car shell's a wheel and it needs to be cut out to a siding in the middle of Utah in the middle of winter. Communication is limited to say the least.
The siding is rarely used and is covered with snow and ice. The switch is a manual switch and is jammed with ice.
A human can deal with getting these issues, cut out the defective car, put the train back together and proceed.
How does a driverless freight train deal with this?
The point here is that exceptions to normal behavior happen all the time. Most of the time, the human pulls to a siding, walks the train and a half-hour/45mins later the train is rolling again.