If I’m not mistaken, God chooses not to prevent evil, so that we can exercise our agency and grow. An argument against that could be “well, if He truly loves us and wants what is best for us He wouldn’t make us go through struggles, and He would make it so we cannot be tempted”. That is simply not why He does it. He does it so that we can make our own choices, and deal with the consequences, be they good or bad. One day, after Judgement, He will banish all Evil into Outer Darkness, and those who were Righteous will live with him. I also want to point out that you have to be really really REALLY evil to be sent to Outer Darkness.
This is all from my religion and what I believe, if it differs from others religions or interpretations of scripture that is fine, of course. “We claim the privilege of worshiping Almighty God, according to the dictates of our own conscience, and allow all men the same privilege, let them worship how, where, or what they may.” This is one of the Articles of Faith in my religion. I am a member of the Church of Jesus Christ of Latter-Day Saints, by the way.