Because the casting out of Satan's minions demonstrates Christ's power over Satan, which will be completed at Calvary.
Col 2:15 Having disarmed principalities and powers, He made a public spectacle of them, triumphing over them in it.
But still though, which seems to be falling on deaf ears, satan isn't bound until his demise in the lof. Assuming Amil, one can't apply his alleged reasons for being bound to that of when he is loosed. When he is loosed, he is no longer bound. This isn't rocket science.
True - but God ALWAYS was more powerful and more sovereign than Satan (which is, what I believe, being demonstrated there). It's God that allows for him to be "loosed". It's not that satan's power overtook God's disarmament of him.
To elaborate - I believe this article articulates it well.....the "battle" between God and Satan:
Quoting from linked article:
Satan, That Ancient Serpent
Who is this serpent? The fullest answer is given in Revelation 12:9: “The great dragon was thrown down, that ancient serpent, who is called the devil and Satan, the deceiver of the whole world—he was thrown down to the earth, and his angels were thrown down with him.”
So, the serpent in the garden is the devil (which means
slanderer), and Satan (which means
accuser), and the deceiver of the whole world. Jesus calls him “the evil one” (Matthew 13:19) and “the ruler of this world” (John 12:31; 14:30; 16:11). The Pharisees call him “Beelzebub, the prince of demons” (Matthew 12:24). Paul calls him “the god of this age” (2 Corinthians 4:4) and “the prince of the power of the air” (Ephesians 2:2).
That’s the one we meet in Genesis 3. He is already evil, already a deceiver, already a murderer when he appears in the garden of God. In Genesis 3:15,
God speaks to the serpent and pronounces judgment on him: “I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel.”
Notice that at first it looks like the warfare will be between two offsprings: “between your offspring and her offspring.” But in the next words something different is said:
“He shall bruise your head.” Who is “he”? Answer: the woman’s offspring. Who is “your” (“he shall bruise your head”)? Answer: the serpent himself, not his offspring.
The Crushing of Satan at the Cross
The day is coming, God says, when
you (not just your offspring) will be defeated and removed from the earth. The offspring of this woman will crush you (see Romans 16:20 and Hebrews 2:14). That decisive blow was struck by the perfect offspring of the woman, Jesus Christ, when He died on the cross. This is one of the reasons why the eternal Son of God had to become a man—because it was the offspring of the
woman who would crush Satan.
Colossians 2:14–15 describes what God did for those who trust His Son, when Christ died on the cross: “[The record of debt that stood against us] he set aside, nailing it to the cross.
He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him.”
When Christ died for our sins, Satan was disarmed and defeated.
The one eternally destructive weapon that he had was stripped from his hand, namely, his accusation before God that we are guilty and should perish with him. When Christ died, that accusation was nullified.
All those who entrust themselves to Christ will never perish.
Satan cannot separate them from the love of God in Christ (Romans 8:37–39).
The little books of Jude and 2 Peter in the New Testament give us clues as to what happened. Jude 1:6 says, “The angels who did not stay within their own position of authority, but left their proper dwelling, he has kept in eternal chains under gloomy darkness until the judgment of the great day.” And 2 Peter 2:4 says, “God did not spare angels when they sinned, but cast them into hell and committed them to chains of gloomy darkness to be kept until the judgment.”
It appears then that once there was a host of holy angels. And some of them, including Satan, “sinned,” or as Jude 1:6 says, “did not stay within their own position of authority.” In other words, the sin was a kind of insurrection. A desire for more power and more authority than they were appointed
by God and
under God. So Satan originates as a created angel who, with other angels, rebel against God, reject Him as their all-satisfying king and joy, and set out on a course of self-exaltation and presumed self-determination. They do not want to be subordinate. They do not want to be sent by God to serve others (Hebrews 1:14). They want to have authority over themselves and exalt themselves above God.
Why would a perfectly holy angel in God’s infinitely beautiful presence use his free will to suddenly hate God?
The Biblical Approach
My approach to answering the question of how to think about the origin of Satan’s sin is to
read the whole Bible with the question: How does God relate to Satan’s will? Is God helpless before the will of evil powers? Is there a power outside Himself that limits His rule over them? Or
is God presented throughout the Bible as having the right and the power to restrain Satan anytime He pleases? And if so, why doesn’t He just destroy him?
God’s Sovereign Sway over Satan
Though Satan is called “the ruler of this world” (John 12:31), Daniel 4:17 says, “The Most High is ruler over the realm of mankind, and bestows it on whom he wishes.” And Psalm 33:10 says, “The Lord nullifies the counsel of the nations; he frustrates the plans of the peoples.
The counsel of the Lord stands forever, the plans of His heart from generation to generation.”
~ The Fall of Satan and the Victory of Christ
**I apologize for the wall o'text, but I couldn't figure out what to edit out. It all seems important to me.