Dominique Organista
Dominique Organista voted up Ray Dart's answer

Here's a couple of thoughts.

If the head was bigger it would be heavier and require stronger neck muscles to keep it usable, this would probably unbalance the horse, which is an eating/running machine.

A bigger head would also (probably) be less streamlined, and horses like to run.

Dominique Organista
Dominique Organista voted up Ray Dart's answer

Here's a couple of thoughts.

If the head was bigger it would be heavier and require stronger neck muscles to keep it usable, this would probably unbalance the horse, which is an eating/running machine.

A bigger head would also (probably) be less streamlined, and horses like to run.

Dominique Organista
Dominique Organista voted up Ancient Hippy's answer

Nobody can "make" them look a certain way. Evolution, for some reason, made them develop that way.