The motorist (aka killer) was probably worried about a law suit
If I'm not mistaken, the dog's owner would be liable for any damages, not the other way around. I highly doubt that anyone would purposely hit her dog. If someone's cattle got loose, stampeded across the road, and caused you to have an accident, wouldn't you go to the owner of the cattle and expect compensation? I don't see how that's different than any other loose domesticated animal potentially causing damage to personal property. It would have been nice if the people at least left a note, but were they really responsible for the dog's death? Any way you look at it, it would have been the right thing to do, but you know how people are. It can be traumatic enough just to hit an animal, yet alone facing the heartbroken owner.
I've had a dog get hit before (and a goat), so I know what melba's going through. We lived in the country and didn't keep our dog contained (you've got to give melba points for trying). He would rarely ever leave the back yard, so we simply put a dog house out back and that's where he usually slept. One night at around 3 am someone knocked on the door, but I was half-asleep and didn't pay it much mind. Apparently my parents didn't hear anything because they didn't answer the door either. The next morning when I got on the bus, there lay Rocky on the side of the road.
Although it was a sad day (I had Mom pick me up from school), I didn't really blame the motorist. Even if she didn't attempt to contact us about the dog, I realized that it was our fault for not having him either chained (I'd rather see a dog dead than stuck on a chain), penned (I also think this is a cruel way to keep an animal), fenced, or contained in some other way. Ever since then my parents have had their dogs spayed and neutered, which greatly reduced their urge to roam. They also keep their dogs on their large back porch when no one's home so they can't get into trouble. As for myself, I now have a house dog that's also neutered. If I allow him to get into a situation where an accident may happen, well, that's on me. Not only is there danger on the roads, but from other animals as well. Hopefully that scenario won't present itself.
Melba, I know how traumatic the death of a pet can be, but I always look at it as a learning experience. I have a house full of animals, and when I lose one I try to think of how I can prevent it in the future.