Humanity began in Africa, as did the zebra. Why did we never domesticate it? Why did we instead journey on foot to meet the Eurasian horse and only then mastered and trained an animal for transportation?
CGP Grey explains in his latest video. There are certain characteristics of animals that are necessary to either domesticated or tame (which are two distinct concepts) them. He explains what makes the zebra different from the horse and the elephant different from the grizzly bear.