Why did people choose to never domesticate them? Was it because they couldn't be domesticated?
As with most animals, domestication comes only when humans find a particular use or value in obtaining the services or companionship of some animals. With Przewalski's horse, there just wasn't sufficient interest or need in domesticating it, most noteably because other species of horse were much preffered for their use and companionship.
Almost all animals (ones with at least the slightest bit of intelligence) can be domesticated over time. Sometimes your time and effort runs short, and the animals are abandoned to history or their habitat in the wild. Regards,
