Because the monkeys are suited to their environment. They haven't had the new to change. However, when humans started evolving, they needed to change. We started moving upright, and so our needs changed. We developed bigger and better brains, learned how to use tools, cook our food, tame animals. We evolved to suit our ever changing needs. I can see where your coming from, it does seen confusing. However, it is better to look at science and religion not as 2 completely separate roads, but as 2 roads that eventually merge into one. When you start looking at it, science and religion need each other. There are to many loop holes and "plot twists" if you only look towards religion, and vice versa with science. However, if you combine them, it starts to come together. Science and religion prove each other.