You don't get to be an Ace by destroying tanks, or artillery, or other ground threats. You get to be an Ace by defeating another pilot in a dogfight. That's why the Air Force is reluctant to support the A-10. They want to put all that money into their fighter jets.

Close air support really should be an Army responsibility, but the Air Force doesn't want the other services flying planes. The only reason the Army is allowed to have helicopters, is because they're not "real" airplanes.