Why is it that sometimes, people who are involved in a hit-and-run accident flee from the scene?

It must be because they are ashamed and don't want to face the family members or police. Can you imagine how bad you would feel? I am pretty sure I wouldn't flee from the scene because my conscience would kill me. Plus they usually find the people within a few days anyway. It would even be more embaring to be caught after fleeing the scene.