As I wrote a moment ago, the Enforcer addressed a Vietnam-era notion of what a counterinsurgency (COIN) aircraft should be. Such aircraft were not primarily close-support airplanes or fighter-bombers, per se. COIN airplanes were expected to patrol, keep militants' heads down, and support troops in contact only ocasionally. The US COIN people were heavily influenced by French experience in Indochina and Algeria. The French found propeller-driven types to be more effective than fast jets, because they could loiter over besieged outposts and take their time identifying small bands of insurgents on the ground. The workhorses of the French colonial campaigns were thus the T-6, the T-28, the AD4, and the B-26--the same, WW2-era/WW2-inspired aircraft that became the preferred COIN types in the USAF.
When it came time to replace aging, piston-engined aircraft, propeller turbines in remanufactured, proven WW2 airframes seemed like the obvious choice. Hence the T-28E, the Cavalier Dart-Mustang III, and the Enforcer.
Unfortunately for the companies involved, in the interim, structural updates for overloaded WW2 airframes turned out to be less cheap and more short-lived than than anticipated (wing cracks in re-sparred B-26s/A-26s, etc.). Worse, relatively cheap, new-production COIN types appeared in the OV-10 and A-37. Both had twin-engined reliability, ejection seats for the COIN-preferred, two-man crew, better cockpit visibility, and all the weapons capability needed. The OV-10 even had a modest transport capability.
Post-Vietnam, even the A-37 and OV-10 held little attraction for the services, other than for limited use as observation/FAC types. The Enforcer was thus effectively obsolete long before it tried to compete with the A-10. But its developers had sunk so much of their limited capital into the project that they couldn't/wouldn't eat the loss without a fight.
