"Now, look at the problems that new procurement takes. Political opposition. Opposition from other branches (The A-10, prior to its shining example in Desert Storm, was facing opposition from internal to the Air Force, since it wasn't fast and shiny and didn't kill planes, AND the Army, because, By God, its not the Air Force's job to kill tanks)."
The Air Force doesn't want them because their mission isn't to shoot down other planes, it's (horrors!) to kill things on the ground (icky, ptooey). The Army LOVES them. In fact, every time the Air Force tried to retire them, the Army said fine, give them to us; we'll field them. Oh, and also give us the budget for them.
Well, that goes completely against the rules of empire building. So, the Air Force keeps planes they HATE, and the Army keeps getting less than optimal ground support from the Air Force.
There's more involved (agreement or law? limiting Army fixed wing aircraft to 10000 pounds), but that's the gist.
Brian Bronson