It's just what you get when dogs are exposed to natural selection on survival traits (i.e. the ability to not get eaten). Highly sociable and docile dogs are more likely to get eaten by wolves or whatever the local predator is, so they have personalities closer to a shiba inu, which is a basal breed and known for stubbornness. Despite this they're still dependent on humans so they're not completely feral.

The same thing happens with cats. If you take a kitten from a feral colony of cats it's more likely to be naturally mean.