It's not so much that the dog doesn't understand conceptually. It's that the dog doesn't have the tendency to protect itself relevant to such a circumstance. With humans, part of protecting ourselves is usually conceptually understanding what tools we have to protect ourselves and why we need them on some basic level, so that is why we need to understand. We grapple with tools and the concepts to understand and weild them, as part of our necessary survival and life processes.

When that becomes hideously defective, such as cowardly, insensibly relying on the temporary privilege of a tyrant, or other such massive logical errors or perversions of man's will, those individuals become easy prey for the vicious, strong and weak alike. The most vicious are usually the most weak, but when they have their temporary power, they will kill.