You've just complicated your logistics and added a whole bunch of personnel requirements for the Army to have any significant amount of planes for use in combat. Not to mention, the Army has helicopters to perform this exact same function already.
Well for one, the Army would have to start worrying about bases with full landing strips, pilot training, the bureaucracy and command structure that would be required to run the squadrons. They would need mechanics that know how to repair them, people that know how to arm and refuel them.
You end up doing a good amount of work just to try and protect a very expensive plane from Air Force politics. Ideally, the Air Force would just settle on an inexpensive prop plane that could perform the same missions as the A-10 at much less of the cost.
I'm not knowledgeable on how effective a helicopter is for CAS.
