From The Propaganda Professor:
Although it has virtually nothing going in its favor and has a great many strikes against it, the death penalty has been the default mode essentially all over the world for essentially all of human history. Why is that? The answer is really pretty simple: the death penalty is heavily favored by conservatives, or those who call themselves conservatives (in our day, they are generally right-wing radicals) and they are the ones who make the rules — rules that usually get changed only gradually, thanks to the arduous efforts of liberals and progressives. And the policies favored by conservatives and “conservatives” tend to be based on emotion rather than fact.
I know, I know, that may come as a surprise if you put stock in the standard narrative from the media. (That’s the “liberal” media of course. How do we know? Because the “liberal” media keep telling us.) That’s a narrative to the effect that it’s really those on the left side of the spectrum who act out of emotion rather than reason. You may have heard the cute little mantra “facts don’t care about your feelings”. It was coined as a clever bit of projection by smug right-wingers to make fun of “snowflakes”. But if you want to know who really acts out of emotion rather than reason, all you have to do is take a look at history, both distant and recent.