God did not create a static creation. Rather, it was created with time built-in. It therefore includes processes and events. Furthermore, in the story of Adam and Eve we are told that evil came into the world in time. This implies that evil is not an inherent, primordial feature of the world, nor did it evolve by some natural process. It came, and keeps coming, by the free choice of creatures.
Recall Jesus' parable of the wheat and the tares (weeds). Weeds emerged in the field, along with the wheat. The servants asked the owner, 'Do you want us to go and pull them up?' The owner answered, 'No, because when you are pulling up the weeds, you may root up the wheat with them. Let both grow together until the harvest. Then we will sort them out and destroy the weeds.' (John 13:24ff)
Evidently it is not yet God's will to totally destroy evil from the world in one massive purge. Rather, the redemption of creation is a process, a struggle in which we creatures have an opportunity to participate.
If you want to understand the origin of evil, consult your own
heart.