You might as well ask why God created people in the first place. God is uncreated, eternal and perfect. We are created, mortal and imperfect. No pain can reach God by his nature; by our nature, we can feel pain. That is the answer. Were God to have created a being equal to Himself in any particular, then there would be two gods, and neither of them would be the true God because one was created and, since God was equal to that being it would mean that God also had been created.