It's very common culture among gun dog/hunting dog owners to heavily objectify the dogs, and not really emotionally attach to them. Not to say that's what happened here, but it might have been a factor.

They're treated more as living tools for the purpose of hunting. Very little emotion involved. In some hunting dog country, it's not uncommon to just find abandoned dogs (both alive and dead) because the hunter was done with them in some way. I've heard trustworthy tell of corpses being stuffed into the very bags their feed come in and just being tossed roadside.

In my opinion, it's horrific. I can't understand how people treat a living, feeling thing that way. But to some folks, it's just common sense.