Zimbabwe also has a low population density and an economy strongly tied to resource extraction, so those two factors by themselves don't fully account for the relative prosperity of Botswana and Namibia.
Of course not, but I'm saying they help. Note how low density countries tend to be either horrible (West Africa) or wonderful (Iceland) places to live.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.