Weapons die for all kinds of different reasons.  Sometimes they happen at the wrong time, either in the midst of defense austerity or with the wrong constellation of personnel.  Sometimes they fall victim to the byzantine bureaucracy of the Pentagon, or to turf fights between the services.  And sometimes they die because they were a bad idea in the first place.  For the same reasons, bad defense systems can often survive the most inept management if they fill a particular niche well enough.