The answer seems to be that only humans are created in the image of God, with a soul that accountable to God. Angels are one order of creatures and humans are another. Angels can obey or disobey, but they evidently do not have “souls” in the sense that humans do.
Nowhere in the Bible is there the slightest evidence that fallen angels could repent of their rebellion. The gospel message goes out to humans made in God’s image. The angels watch the unfolding mystery of salvation with wonder (Ephesians 3:10 and 1 Peter 1:10-12), but they are not among the redeemed.
See Why Doesn’t God Give the Fallen Angels a Chance to Repent?