The reason involves the ascent of science and the development of an increasingly secular society. Decisions involving the giving and taking of life figure prominently in this paradox. Throughout history, the primary obstacle to advances in these kinds of decisions has been waged by organized religion. Human dissection was forbidden a millennium ago, yet its use has actually extended and enhanced rather than detracted from life. Even Luther Burbank, the great botanical experimenter whose hybridization of plants was condemned by organized religion, paradoxically, his work has provided additional foodstuff that has saved untold millions of lives.
Science marches on.
The key problem is one of economics. The difficulty in lesser developed countries is their individual responsibility for taking full charge of life's challenges. There is much to be done in terms of bringing lesser developed countries into a new phase of modern day affluence. For the meantime, the U.S. Criminal jurisprudence criminal system will continue to use punishment as a deterrent to runaway crime. More people, not fewer, will be imprisoned.