A: For the same reason He doesn’t destroy us. He loves him.
What? God loves Satan?
Yup. But He absolutely hates what Satan does.
«But,» you say, «if God had destroyed him, all the pain and suffering in the world would never have happened.» I take that to mean that if God knows your great-grandson or great-grand-daughter is going to murder a neighbor, He should come down and destroy you right this minute so it won’t happen.
«Wait a minute,» you protest. «I don’t want God to kill me off because of something a future relative is going to do.»
Exactly. If He’d destroyed Satan back there in Eden, the whole universe would see how unfair that was. Instead, Jesus told His Father, «Let Me die. Let Me pay the price for Satan’s sin, and for everyone’s sin. Then death will be only a sleep, and all those who choose to love and obey You will have a bright future waiting beyond the grave.»
Satan will ultimately be destroyed along with those who follow him and turn their backs on God’s forgiving grace. But it will happen only after everyone, including you and me, has had a chance to choose which side they’re on, and which future they want—eternal life or eternal death.
«For sin shall no longer be your master, because you are not under the law, but under grace» (Romans 6:14). Choose grace!