I really should be working, but a third point occurs to me.

3. Again from a structural point of view, the pyramids may look like they do because the insurgent has a severely limited menu of tactical options to choose from, a slightly wider range of operational styles to work within, and far greater liberty to define an overall strategy than his conventional opponent. At least from a military viewpoint, the COIN strategy is defined by political masters and can only be changed or modified with great effort. Operational options in COIN are often constrained by host nation concerns, resource constraints, requirements to integrate with other agencies and allies, etc. On the other hand, the conventional forces normally have a wide variety of tactics, techniques, and procedures to choose from. So it may be as simple as the fact that humans tend to focus on those things they actually have some control over. As my sainted grandmother said, "when there is no option, there is no problem."