Great question! This greatly depends on what you mean by 'you'. Why are we who we are? If we're talking about personality, that is shaped through an interaction of two factors, inherited tendencies and environment. Or you could be asking Why am I here? Which, in a larger sense, is asking Why are any of us here? What is the meaning of life? What is the significance of living or existence in general? What is our purpose? To seek wisdom and knowledge? To achieve biological perfection? To create great and astounding new flavors of Oreo cookies?
So you're going to have to get specific, Socrates, why what?