I once slammed into a German Shepherd dog on a dark rainy night. I was driving a small car on one of those steeply banked 2-lane roads that are outside the main city of Houston. I was not speeding (indeed traffic was almost a crawl because the heavy rain made it almost impossible to see anything), as it was raining so hard I just wanted to stay on the road. As I'm driving, the German Shepherd appeared in front of me and pulled the "deer in the headlights" routine. I tried to slow down as best I could, but did not want to go down the embankment or hit the cars coming at me in the other lane (which an attempt at a complete stop would have caused), so I braced myself and hit the dog and knocked him down into the ditch by the embankment. Even though I was going quite slow, the car had more torque than the poor dog.
As a dog lover, I was concerned, so I drove around the block to see if I could help (I could hear the dog yelping after I hit him). As I came around, with my window down, I could see and hear people crowding around the dog from the house where the dog was hit. Whether they were the owners or not, I don't know, but I was hearing stuff like "some sumbitch musta hit 'im and kept a'goin!". I decided there was nothing I could do, so I went on my way. Those country types who let their dogs run loose are not to be messed with, IMO.
It still bothers me that I hit that dog, even though there was no way to avoid it without endangering my life or those of other drivers. I can still see the accident and hear him yelp as he ran off in the ditch. How someone could hit a human being and not react at all is amazing.
I have hit a dog and a cat (thankfully no people but came very close once to hitting a child). While I don't like injuring animals, animals are not people. If I have the means to avoid them, I will. But if I don't because of traffic or other conditions, I just have to hit them and live with the consequences.
That happened once with a cat that ran into the street and under my tires. I could see the cat in my rear view mirror flopping around in pain but I could tell it wasn't going to live long. When I got to the stoplight, some old woman started honking her horn and cursing at me as if I had chosen to murder some innocent kitty cat.
Motor vehicles rule the road. Nothing has priority over a motor vehicle on the road. If you don't think that way, you'll never go faster than 20 mph.
The sort of people who run across big freeways at night are likely to have pretty rough associates. If some of the drivers realized what they'd hit was human, their reasons for not stopping may have been similar to yours (in addition to the extreme danger of stopping on a freeway).