That one’s in part because cruelty is by design I imagine, but also because the people giving those injections aren’t medical professionals and can’t legally obtain those substances. Guess that also explains how they can fuck up finding veins this bad. From what I’ve read and heard (In Last Week Tonight among others, I believe) they basically just use toxic crap that chemically burns the inmate from the inside and makes them asphyxiate while conscious. And of course they turn out to be undeserving of an execution around 5% of the time.