Why did God not just ban ananias and sapphira from the church?

In devising and implementing their lie, Ananias and Sephira had separated themselves from fellowship with God and the believers.

Acts 5:3 "But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land?"

Peter's question to Ananias gave him a clear path back to fellowship. Had Ananias been courageous enough to face the truth, the result would have been joyous healing.

I John 1:7,9 "But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness."

God did not bring about Ananias and Sephira's death. The Devil, who holds the power of death, had orchestrated this ensnarement. God's desire was for them to believe to live and have further opportunity to cast off the works of darkness.

James 1:13-15 "Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man: But every man is tempted, when he is drawn away of his own lust, and enticed. Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death."