Roadkill

OK here is what I don't get, why is the road kill always on the side of the road?

Do people swerve onto the shoulder to hit the animals?
Do people hit the animals on major highways and then stop their car and move it to the side of the road?
Do they hire people to move them to the side of the road?

If its the last one why don't they dispose of the animal instead so that people don't have to see bloody split apart animals? Alternately if its the second one that doesn't seem very safe to me for a number of reasons. And the first one doesn't seem likely because I don't think that many people have trouble staying on the main parts of the road.....which brings me back to my first question: how does it get there???