Why do parents cover up for their children's mistakes?? Doesn't this hurt more than it helps in the long run?

What ever happend to parents who corrected children when they were on the wrong path. I know of this old man that is still covering for his bad boy who is now in his 40's. The boy has been in and out of prison and the dad still covers for him. Wouldn't a truly loving father kick his backside on to a better path?