Well the upgrade program has been underway for some time, adding more functionality and digitalising the cockpit. Actually, I think the upgrade has been scaled back due to budget constraints. This contract is just for the wing replacements which are needed to keep them flying safely.
The aircraft is too specialised, and was actually set to retire at the time of the first gulf war. It proved itself and stayed in service. However production lines were closed now it had proven itself. Also Fairchild made a shift in its business, so it probably wasn't marketed very much. For potential customers it is just too specialised. It can virtually only do CAS and some interdiction... until the upgrade now, it was not even an all-weather type and only guided weapon being the Maverick as far as I know. Most air forces can't afford a dedicated CAS platform, even the easier to operate and maintain Su-25 didn't remain long in service with most East-European countries after the curtain fell. In addition I reckon the Americans did not want to sell this weapon to just anyone, because of the GAU-8 Avenger. Also I think it is quite expensive to operate compared to other CAS aircraft such as the "attack trainers", AMX, Su-25, etc. And for years it seemed attack helicopters would be better suited.