It's pretty much torture in many, MANY prison systems. Not to mention overused solitary confinement which is literal torture. So being tortured for your entire life instead of killed seems like a much harsher and inhumane punishment. Not to mention the guard abuse, abuse from others, etc...
There is also no restitution for losing 20-40 years of your life in a failed system.
Especially because the system is literally rigged against those who do possibly get out after being proved innocent.