Because not everything is as simple as "he was a bad man and got what he deserved". Sure, there are a lot of people out there who would be largely improved by a lead salad or two or more. Sometimes you do some phenomenally shitty things to people, but if that was always enough to earn you the capital punishment, I'd be long gone by now.

[It's hard to judge someone who controlled her life for so long when there are so many lives Rey has ruined, herself.]