BS”D
Hashem created the shell that way so that human beings, who are tachlis habriyah, could easily find a way to open it and therefore make the nutrients and taste of the pistachio easily accessible. This has nothing to do with careless, amoral evolution and the survival of the fittest.
(It is interesting that when Khomeini YMS took over in Iran, which I remember very well, the US pistachio supply was not interrupted for very long as first California and then I believe Turkey took up the slack).