Why do some people get sentenced 100+ years in prison when they don't even live that long? While others get sentenced to death? Wouldn't it make more sense to just do that?
Because it comes with a certain period when they're eligible for parole. So by giving them a long "sentence," they won't be eligible for parole for a long time. So when someone gets 150 years as sentence, it means he'll be long dead before he's eligible for parole. No one actually expects him to do the 150.