Because in California death row is nothing but a big money pit. There are many problems with the death penalty, such as executing an innocent person. That's an obvious one. But there are problems that aren't so obvious and they don't just bring harm to one innocent person, but to all of society. California is a perfect example of how the criminal justice system has abused the death penalty to the point that its a broken joke. Killers in California actually prefer death row because they know that they will never see the needle or any other form of capital punishment.
Unfortunately the death penalty debate is usually an emotional debate based on an eye for an eye justice, which blinds people to the real facts which are it costs too much, it doesn't deter future crimes and authorities can't be trusted not to abuse it.