It's not some liberal conspiracy to drive up costs of trials, it's to prevent innocent people from being executed.
"And I just think the big challenge with America's death penalty has been its unreliability. We've now seen 158 people released from death row after being proved innocent. That means for every nine people we've executed, we've identified one innocent person. That's a pretty shocking rate of error."
http://www.npr.org/2017/05/01/526436000/after-arkansas-executions-lawyer-criticizes-use-of-capital-punishment