The U.S. Air Force will no longer give the Good Conduct Medial to enlisted troops. The reason is simple, there are too few air force personnel who don't qualify for it. Since these awards are supposed to distinguish exceptional behavior, the Good Conduct Medal has, in effect, outlived its usefulness.
Since 1941, the U.S. Army (and the U.S. Army Air Force, which became independent in 1947) has been handing out the Good Conduct Medal. The award was given to troops who served for at least three years, and didn't get into trouble. The intention was to encourage a largely conscript force, many of whom didn't want to be in uniform, to behave themselves. It never really worked, at least it did not have a major impact on troop behavior. It did make it easy, when veteran troops were wearing their dress uniforms, to pick out those who had not been in trouble.
The U.S. military has been all volunteer since 1972. But, for all practical purposes, the U.S. Air Force has been all volunteer since the end of World War II. Even with the draft, there were still plenty of young men and women willing to volunteer. And given a choice between the high tech, and more comfortable air force, and the army, a disproportionate number of the volunteers went to the air force. The air force rarely had to take any draftees after World War II. Since everyone was a volunteer, that created a much more disciplined, and well behaved, force. A force that no longer needs a medal to tell them they are well behaved.