Why do people who believe in this still commit sins? Sins are not good works.
As long as a believer is on earth, he or she will sin, since they have the physical body that it enlivened with the life of Adam in them.
At salvation, the life of Christ is added to a believer.
At death or translation, the earthly body and its life of Adam is done away with and the believer will have the life of Christ. No more sin nature.
Paul describes this well in Romans 7.