It’s because those types of dogs are built to be unstoppable, gotta be able to handle alot of abuse when your a herding dog.

A Collie, a Sheppard and a pom go into the forest. The pom comes back covered in blood, the collie comes back covered in blood with a cougars leg in his mouth and the Sheppard comes back covered in blood and guts. Teamwork makes the dream work.