Death penalty sounds a lot like revenge, plus it takes so long for all the legal work to go through that a lot of times i think the person on death row just dies in jail anyway. Removing the death penalty would save a lot of legal work and money im betting, and with that extra money they could put it into making prisons more secure, so people having a life sentence or something would not be able to escape.
At least, thats how it works out in my mind, not sure about what would happen irl.