Limitation or design limit.
Your catching on. and your right, you can't "throw it about as much" but a robotic pilot would not "throw it about as much" anyway that what meatbags do! autopilot is just that for getting from A to B usually by the shortest route, but occasionally via defined waypoints for air corridors or to avoid trouble spots or heavily populated areas.
No one has invented a self aware combat robot yet. that is able to dodge bullets and rockets.. That job is exclusively for meatbags or Hollywood. War zones are usually very quiet combat is usually limited to sporadic burst in certain (usually populated) areas. These days supply lines just avoid those areas. the problem is that Roads go straight to these areas.. So you are taking about 30 minutes airborne and zero small arms hits rather than 15 minutes direct and 10 hits.
You should also realise that a slung load can be loaded and dropped off in only 30 seconds or so. which is highly advantageous when you are shipping back and forth. an internal load requires 20 minutes on the ground at each end.. if you are shipping 30 crates on a 30 minute flight.. I'll let you do the maths.
The Darpa Grand challenge was set up to develop robotic trucks for robotic delivery tasks, but that only works in situations where you have army vs army with defined front lines and where it is safe behind the line. The wars we are fighting now are not like that there is no front line as such fighting can and does break out anywhere, even in areas that were safe the day before. this is the problem with an Embedded Enemy. so the Darpa Robotic Trucks would be useless! hence the need to fly supplies, with a device like the kmax .