Why punish attempted murder less than murder?

Because the attempted murderer could be reformed, and there is a possibility that nobody was truly hurt in the attempt

It is usually less because the attempt wast successful. Although it really shouldn't be that way as it both had the same intent and they carried out with it but Attempted Murder mostly means your attempt fails. The sentence should be the same but since no life was lost it is a less sentence. Sometimes its not as a lot of times people can receive life without parole for both crimes. It always depends on how they do it and the ending.