Yeah, I did mix-up what you meant there. My bad.
And I remember thinking that was freakishly counter-intuitive as well when I first learned it, but unless some new studies have come out since I completed my CJ degree and short career in law enforcement, this is what they are teaching.
It's all about the cost of the appeals since a lot of the guys have public defenders - preparing the prosecution and defense on the appeals, and a lot of states have multiple mandatory appeals on death penalty cases, run into the millions.