Why does the enzyme pepsin (present in the stomach) denature in the intestine?

Pepsin is an enzyme that breaks down proteins. Produced in the stomach, pepsin becomes inactive at pH values of 6.5 or more, but it is not fully denatured until it is in an environment with a pH of 8.0. Bile in the small intestine increases the pH value of food from the stomach to make them alkaline, which denatures pepsin.