I realize most city dwellers either use guns for very occasional hunting or for home protection. But not all people are city dwellers, and the needs of all are not the same. My son killed two feral hogs with a semi-automatic rifle out in the country recently. Feral hogs are enormously damaging to farming or ranching, and are dangerous to humans. In places like Texas or Louisiana, they are pervasive. Armadillos dig holes in fields that livestock can break a leg in and that can cause a person driving a pickup to damage his vehicle or be injured himself. Same with groundhogs. Coyotes or feral dogs can kill young livestock, and do. Some animals can be rabid. One doesn’t have to be very far into the countryside to be exposed to animal threats. And, of course, if one is a crack shot and never misses, one could get by with a single-shot or a small magazine. But not even good shots are “special forces sniper” quality.
An AR-15 is lightweight, easy to manage, easy to store away, and effective when it comes to some of the abovementioned critters. Perhaps some people buy ARs or other “military-style” weapons for their appearance, but to a country person, they have considerable utility. They were not designed for the military in order to look threatening. They were designed the way they are for utilitarian functioning; functioning that can also be applied to civilian life.