Basically because there is unhealed energy present within your being.
Your energy gives rise to your thoughts and your thoughts alter your energy. They are inseparable.
Much of our energy is unconscious (we're unaware of it) and running on autopilot. Enlightenment isn't a self-improvement course. It's not a positive thinking class. It has nothing to do with your thoughts although the energy of your thoughts may certainly change as a by-product of your awakening.
Awakening is about bringing awareness to the fullness of what you are and seeing beyond your identity as a limited self.
Awareness itself is the most powerful transformative tool you have. What you resist persists. aka, what you go unconscious to and are unwilling to face and bring awareness to, that's what persists. On the other hand, what you look at disappears. By shining the light of awareness on your darkness and facing your inner demons and fears, awareness itself automatically transmutes the energy back into light.
So the key is to SEE. Bring awareness to your darkness. See yourself as you actually are, without judging any aspect of what is seen. Accept it and love it. Be open, honest, and sincere about what is. Want to see the Truth more than you want to be right, feel safe, or be comfortable. You gotta want to see Reality. When you want it bad enough and are willing to face the darkness within, you will see the Light that was always there, the being that you truly are.
