If Jesus defeated Satan at the resurrection, why is Satan still called the god of this world?
Christ's resurrection won the victory over Satan in potential, but Satan is not yet under Christ's feet. He remains the God of this world and still destroys lives. Christ sits at the Father's right hand until God makes His enemies His footstool, so Satan's final subjection is still future.
Les explains that as soon as God revealed to Satan that the seed of the woman would deal with Satan's powers, defeat them, and crush them, that defeat was accomplished at the cross so far as the potential. But even after Christ was raised from the dead victoriously over a defeated Satan, Satan is still the God of this world. He is still destroying lives, and he is not yet under Christ's feet. Christ is to sit at the Father's right hand until His enemies are made His footstool. Hebrews shows that Christ has accomplished the work of the cross and has risen from the dead, which is why the context spends so much time in 1 Corinthians 15.