Because self defense is not in the cultural lexicon of the average American. As far as Joe and Jane Public are concerned, Officer Tim needs a gun for his job and Pharmacist Tim does not. Thats why we see rulings like this;the judges first reaction to the concept that ordinary people need an AR15 is incredulity, not acceptance.
At one point in my studies ,I took a class being taught by a sitting Federal judge. One day the topic was about the Supreme Court of the US, and how they resolve conflicts between ciruit splits. After the lesson he opened the floor for questions.
I asked a question about why it was that the SCOTUS hadnt resolved the 7th Circuit ruling in favor of CCW in IL compared to the various rulings against the same elsewhere.
His answer essentially was that he owned a bolt actiom rifle and shotgun, voted Democrat, liked guns, but that some issues need to be left to the states to decide and that differences in gun laws were a consequence we had to live with for the greater good. Se'f defense? He didnt even know what that meant with regard to specific use of firearms.