The State of California commuted Charles Manson's death sentence to life in prison as a result of the US Supreme Court's 1972 ruling in Furman v. Georgia regarding the application of the death penalty.
One of the
many reasons California is a joke.
You might want to read the Court's opinion which was rendered in response to several cases none of which was a california case. As typically happens, the Court remanded those cases for further proceedings consistent with the Court's opinion. In light of the Court's opinion, the State of California could anticipate a large number of appellate hearings based on that opinion thus tying up significant State resources. Further, the necessity for a revision in california criminal statutes and the challenges to their compatibility with the Court's opinion would have simply achieved what the commutation of Manson's sentence achieved.