There just aren’t any more that are worth our time. It’s actually pretty difficult to find species that suit domestication—although there are a few exceptions, they generally need to mature quickly relative to us, be willing to breed in captivity, be able to eat the food we can provide, have a good temperament, recognize humans as their pack leaders, and not flee when they’re scared.So, although we probably could domesticate some seemingly good candidates, like zebras or deer, they’re better off in the wild.