Why are introverts so shy?

Understanding the Difference Between Shyness and Introversion

Many people confuse shyness with introversion. However, they are not the same. Shyness is characterized by a fear of being negatively judged by others, which is somewhat similar to social anxiety. In contrast, introversion is defined by a predisposition to feel overwhelmed by too much external stimulation and a need for solitude in order to recharge one's energy.