The reason that attempted murder is a lesser charge than murder is the fact that in an attempted murder it was just attempted and nobody died.
As for murder the charge is more severe and the penalty more severe because of the fact that someone died because the person actually succeeded in murdering the person.
Even though a lot of people think that attempted murder and murder should be charged the same way because they are trying to murder someone and may do it again.
The thing is that some people can change and just had a bad though to try and murder someone and it's best they didn't follow through with it or succeed in murdering the person.
So attempted murder can get you off on 15 or 20 years in prison or even sometimes less time in prison while a murder charge can get you 25 years to life in prison or even the death penalty.