AVs were created to deploy land vehicles on unfamiliar planets with incredibly varied terrain, but were soon adapted to environments outside of their original purpose. This adaption was part necessity and part familiarity, as the Exodus ships of humanity had limited materiel and personnel. It was easier and cheaper to modify already manufactured AVs than create ones from scratch. This approach was encouraged by the small pool of pilots most ships had available, and the introduction of the Predictive Control program (or Pre-Con), which builds on an AV’s familiarity with its pilot, reinforced this doctrine. Even after the Sovereigns were established and had the resources and people necessary to have more specialized models, many can still trace some aspect of their design back to the AVs of old.
The meaning of AV has changed over time. Originally short for "Armored Walking Vehicles," it was the acronym for the massive, walking, military vehicles used by Sovereigns. But as the civilian populations became more familiar with them, AV became a catch all term for any vehicle with sufficient gravitas—whether bipedal vehicles, massive tanks, or fighter-bombers. This trend was especially true for vehicles that blurred the line between those distinctions, such as submarines that could deploy legs and move on land.
As so often happens with military technology, civilian AVs were made available to those outside the military. Civilian Vehicles (or CVs) are a very niche product. Individuals who can afford them use them as a status symbol; there's nothing quite like getting stuck in traffic in your 30-foot bipedal vehicle. Companies often purchase specialized versions for industrial uses: farming, mining, heavy cargo transport, and many others. In most cases, the military-quality parts are swapped for less expensive versions that will live up to the wear and tear their civilian owners put them through, but it's not unusual for the desperate to take them to war.