The issue is simple: these companies have used the public domain nature of their work as their primary defense against lawsuits for damage caused by their products. I can think of several notorious issues off the top of my head:
In each of these cases, the courts agreed with the contractor's arguments that the product was built for the military, to the military's specifications, and that the proper defendant was the military. This saved the contractors billions of dollars of liability.
Now, they're VOLUNTARILY casting aside that defense. It will be cited in any future cases as "admission against interest," and open the door to any number of lawsuits when someone's house winds up stopping (or at least slowing down) a military aircraft.
Your points are well taken. (I never took a different view in any post)