Pins have a consequence for non-compliance, that consequence is often discomfort at best and can be unconsciousness, skeletal injury, muscular injury or nervous system injury. These consequences are often too severe for civilian enforcement groups to entertain so traditional pinning solutions may not work for these groups.
Great post Jon. Pins are not used very commonly outside of the dojo, and the reason is what you stated. There's very specific purposes for a pin, but even at that, it comes with an inherent risk of severe injury. If you are concerned about seriously injuring someone, then you wouldn't want to use a pin.
Really, a pin in and of itself doesn't make sense. Why only temporarily restrain your opponent with a pin, when you could deliver a crippling blow or joint lock which would more effectively acheive submission? To me, the pin MUST be partnered with pain, or at least the imminent threat of additional pain. Otherwise it amounts to little more than creating a brief haitus in the conflict, with the oppoenent eagerly waiting for you to release him from the pin, which you would eventually have to do.