I think it's because it's the law to use clean needles.. That would be my guess. Wow, I like how it's just a poll and people are flipping out? Calm down, geez.
In case the condemned receives a stay of execution at the last minute.
Since no one knows if the condemned will be receive a stay at the last minute, standard medical infection rules apply. This includes swabbing the IV area with alcohol and iodine as well as using sterile, one-time-use needles.
Actually it is so if the person who is giving the injection gets poked they are safer...and I suppose it would be difficult to buy legal "unsteryl" syringes lol