Why doesn't Satan repent?
Satan cannot repent because the Lord has not granted him repentance. Only when the Lord grants repentance will it happen, as Paul teaches:
The repentance that leads to salvation and a changed heart is a work done by God alone in the heart of a person, so unless God grants repentance, a person (or angel) cannot repent of sin.
Furthermore, the Bible says it is not in God’s plan to grant mercy to fallen angels like Satan:
Therefore, God has no plans to grant repentance to Satan, so therefore he will not ever repent.