What is the logic?

I cannot understand the logic of some jail sentences given by the judges in the USA. The sentences given to the man that shot and killed 6 people and wounded congresswoman Gabrielle Giffords was 7 life sentences plus 140 years.

The New York Times said about the sentence:

TUCSON — Jared L. Loughner was sentenced Thursday to seven consecutive terms of life in prison at a court hearing punctuated by raw emotion as former Representative Gabrielle Giffords and her husband, Mark E. Kelly, for the first time confronted the man who shot her in the head during a rampage last year that left 6 dead and 12 others wounded...

Mr. Loughner’s punishment — in addition to the life terms, he was sentenced to 140 years in prison — came as no surprise. It was a condition of the guilty plea he entered on Aug. 7, admitting to the shootings and bringing to an end a case that had prompted much soul-searching about mental health treatment and the country’s gun laws.

The man must not be susceptible to heart attacks if he didn’t have one upon hearing those sentences. I almost took one just reading about it.

They must have a reason for that kind of sentences but I can’t understand the logic behind it. This is not the first time I've read about prison sentences that makes no sense to me whatsoever. I guess with this kind of sentences, there is no way that this man will ever come out except feet first. So if there were no doubts about his guilt why not execute him? To me it would make more sense to execute him.  Then the families of the loved ones the he killed would know that part of their taxes are not used to support this murderer until he dies.

I might be wrong but that’s the way I look at it.

That’s my rant for the day