Army culture vs Air Force culture
The important difference between Watchkeeper and Air Force drones like Global Hawk is the mentality of the organisation.
In the Air Force, flying is done by Flying Officers, emphasis on Officer. To fly a drone you must be a properly qualified pilot with many hours in the cockpit. Air force drone user interfaces are designed on that assumption; the pilot is controlling the drone second by second, steering it on the correct course and altitude while monitoring airspeed and responding to any unusual situations as pilot in control. The Air Force will not buy a drone which does not require a pilot to fly it.
In the army, operating machinery is done by enlisted men (OK, maybe a few enlisted women as well). Officers have more important things to do. If it is complicated machinery then there may be a two week training course during which time you learn the drill. Hence the Watchkeeper user interface is designed on the assumption that it is going to be operated by someone who doesn't know how to fly, but can press the right buttons. The user enters waypoints on a map using click and drag as instructed by an officer who has decided what needs to be patrolled or surveilled, and the drone handles the aviation part. The Army will not buy a drone which requires a pilot to fly it.
So when something unexpected happens the Watchkeeper operator has no pilot's training to fall back on. Maybe at some point during the 2-week training course the sergeant instructor mentioned what to do if it takes off again after trying to land, but trying to remember exactly what the drill was a year later when it's never happened before is a bit too much to expect. Much easier to decide its gone out of control and hit the kill switch before it reaches somewhere populated.