“Inert Gases are the perfect solution. “
The only reasons I can think of that this method isn’t used is that the people involved in the decision-making are unimaginative, or mired in tradition or dumb as ditch water.
If the judge instructed the prisoner to make a 100% blood donation to the Red Cross, I think that would be sufficient. No noise, little pain when the heart starts struggling and it’s done.
More likely is that there would be very little money to be made for friends and family.