Negative Camber Doesn't Seem Right

In theory, if a vehicle was only driven in straight line, on a flat road, zero camber would produce the most even tire wear.

In reality, much of the wear occurs under loaded conditions (hard turns) and the combination of camber and caster help keep the wheel more upright as the body rolls and the weight shifts.
The alignment settings settings recommended by the factory were based on a couple things that have changed. One was high crowned roads were the norm (and unpaved roads still pretty common). The other was bias and cross ply passenger tires, did not require or want a lot of negative camber, and the rubber compounds as a whole were not as high grip as what's become available since the 70s and 80s.

For competition tires, the manufactures publish the recommended alignment settings. Usually this is just camber, but sometimes camber and caster. Final decisions are then made on the track, preferably with a tyre pyrometer. The pyrometer is used to measure temperatures across the treads (the goal being uniformity). For passenger and truck tires, I suspect a manufacturer's rep can provide the recommended camber range for any of their products.