We always get questions why we predominantly use handguns and knives in our ASR classes for drilling. The simple answer is that it is significantly more complicated to defend against a handgun in close quarters than a rifle, and since time is definitely a limiting factor, we want people to address the more complex problem, then be able to apply those concepts to other situations.
We use the long gun in our courses, but if you only focus on the long gun, you can create a false sense a security/control that may not be there when dealing with a different weapon. We feel, addressing the handgun allows us the easiest transition to other situations.
Check out the video and see what you think!