I see no practical purpose to breed those things. Besides pets. They have no use. They are smaller than a goat, or as small as a goat. If their turned loose into a range (ranch) conditions, they will be some well fed and trained wolves, feral dogs, coyote or in Australia dingos. I have seen some miniature cattle that are about half the size of regular breeds of cattle.
The "reason" is so people can produce beef on a smaller scale than regular sized counterparts. But still the photo that you showed are smaller than that. I just don't buy it. The smaller size doesn't have the range ablity of the larger one, in the ability to protect itself from preditors.