Because God wants us to save, Jesus came here to save and seek the lost, He gave His own begotten Son just to cleanse our sin/evilness, God gave us the chance because of His wonderfu love to us. Thats why, God wants us to go to Him to earn the salvation that is freely given to us.
Evil is in everyone of us in this world and sometimes, it is in small doses. If God is suppose to be destroying all the evil in the world, then the whole Human race is going to be extinct and since he doesn't want that he has given us what i term to be a very long rope and tolerance.