I think that may have more to do with how horses are used as domesticated animals. They're like dogs in that they need to understand commands and like dogs the survival of their human depends on the animal so the animals were likely bred to be social and able to take ques. Also a huge thing with horses is getting them to be less excitable and willing to do whatever the human tells them to do. Horses do NOT naturally ride into battle, but they can with the right training and condition.

Basically they're not like farm animals who exist to mostly do simple work or for food. Horses needed to understand complex commands so they were bred to be able to read humans extremely well. Way more so than say a cow or sheep.