Development contracts have begun to convert old F-16s into drones (QF-16) as replacement for old QF-4s based on Vietnam era F-4s. These drones are used for target practice and radar decoys, for pilot training, SAM/radar testing and Airborne missile testing. The F-4 was never a very good aircraft and its poor handling and lack of engine production has caused the AirForce to look elsewhere. Initially, six F-16s will be converted, but the AirForce plans to aquire at least 220 over time.
Another aspect is the possibility future combat may include sacrificial waves of unmanned drones as bombers. Recent war game analysis of a combat with China showed conversions of their old Migs could drain defensive systems. The ability to convert old F-16s, as well as F-15s, in the same manner is something the US has had at its disposal. There's also no shortage of these aircraft, as the 3rd-largest air force on Earth is America's boneyard.