Christ Longsuffering Satan's Evil for Greater Honor

Here is how John Piper answers the question, "Why does not God just wipe out Satan?"

"Why, then, does God not simply wipe Satan out? He has the right and power to do this. And Revelation 20:10 says he is going to do it some day. Why didn’t he cast him into the Lake of Fire the day after he rebelled? Why let him rampage through humanity for centuries?

The ultimate answer, as we saw last week, is that “all things were created through Christ and for Christ” (Colossians 1:16). The Son of God, Jesus Christ, will be more highly honored in the end because he defeats Satan through longsuffering, patience, humility, servanthood, suffering, and death, rather than through raw power. And the more highly honored the Son is, the greater the joy of those who love him."

Source: "The Fall of Satan and the Victory of Christ"