Airlines, Airplanes, Airports

The famous MD-80. A great plane, until American and Delta Airlines grounded all of them delaying and cancelling all flights that used MD-80’s. Unsecured wires was the problem the FAA had with the MD-80’s so most traveler’s were very unhappy. What somebody needs to explain to me is #1 Why this problems was not solved when the FAA did its overall tests? and #2 Why was this not taken care of when the plane was built? Not only that, but American’s fleet has more MD-80’s than any other aircraft.