Why do Protestants reject the doctrine of the Sacrament of Penance?

Why do Protestants reject the doctrine of the Sacrament of Penance? This is the sacrament of where the faithful confesses his or her sins to a priest, and the priest gives spiritual adivce, gives him or her a penance, and then absolves the sinner. On Easter Sunday, Jesus breathed on His Apostles and said, "receive ye the Holy Ghost, whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained." (John 20:22-23) See here the commission, stamped by the broad seal of heaven, by virtue of which the pastors of Christ's church absolve repenting sinners upon their confession.