Because the liberals/socialists/racists WANT there to be AS MANY failures and errors and AS MUCH pain as possible so they can eliminate capital punishment ... while aborting as many babies as possible!
Bingo. Their goal is the elimination of the death penalty.
And instead of doing the hard work in the political arena to convince a majority to agree with them, they are doing the typical Lib thing and playing cute manipulation games to get their way.
Vilify hangings, firing squads and the electric chair as barbaric. Granted the visuals do lend themselves to that. Make State Legislators afraid to go anywhere near them.
Then go after the gas chamber. Draw uncomfortable parallels with Auschwitz. You can get States to drop that one like a hot potato with an effective PR campaign.
That leaves the scientifically modern, “humane” method of lethal injection. Use intimidation tactics to shut off all possible supplies of the drugs, and you’ll have achieved your objective.