Allow me.
"Either God wants to abolish evil, and cannot; or he can, but does not want to. If he wants to, but cannot, he is impotent. If he can, but does not want to, he is wicked. If God can abolish evil, and God really wants to do it, why is there evil in the world?"
I already explained why above. I quote myself here.
"Because sin had entered the world, and into the very nature of man through Adams transgression, then for God to destroy Satan, he would also have had to destroy the man he loved".