The act was not carried out. The loss of a life can change many factors. Say the victim had a family to support, the last of a bloodline in a family, or won't be there to train their grandchildren to ride a bike. The attempted victim still has all that to look forward to.
Attempted murder is the exact same as murder when it comes to the criminals mind-set. If you aim to shoot someone in the head and miss on accident, you are just as guilty and dangerous to society as if you were a better shot. Attempted or succeeded, you need to be rehabilitated just the same. The person who missed doesn't need to be rehabilitated less than the person who hit.