Earlier quoted context omitted.
This is one of many reasons we will still need humans present, if only in a guard capacity.
If a cargo was valuable enough, a driver's life would only be a collateral damage. Furthermore, all (non military or security) personnel training programs I've encountered specifically highlights, that in a case of armed robbery, do not resist, obey and do not escalate conflict in any other manner while trying to call help unnoticed.
Do you take the guard hostage? Do you kill them? Will they themselves be armed? Will they put up a fight, training or no training? If you try aggressively to bring their vehicle to a halt, will they concede immediately (as an autonomous vehicle likely would), or will they try ramming your vehicle?
A human guard is an unknown quantity, and any crimes you commit against their person are in a different league to the theft of the cargo.