Same reason paleontology, geology, anthropology, climate science, astronomy, and so on have a difficult time... Any theory that can't be falsified by running a

Same reason paleontology, geology, anthropology, climate science, astronomy, and so on have a difficult time... Any theory that can't be falsified by running an experiment shouldn't be called "science". At best, people pick the theories they believe because they "fit" existing observations, not because it's good science. (No computer models really aren't good enough - you have to ask whether the model was correct and included all the important components)