Invalid reasons for why a character should not be redeemed:
They’re too evil! - Redemption has nothing to do with how good or evil you were to begin with.
They don’t deserve it! - Redemption is not something that can be “deserved.”
Their actions are unforgivable! - Redemption has nothing to do with forgiveness.
It’s too late for them to change! - It is only “too late” to choose redemption when a character is dead (unless the scope of the story includes an afterlife in which change is possible).
Valid reasons for why a character should not be redeemed:
It doesn’t fit the themes of the story.
They’re not an important enough character for showing the process of a redemption arc to be worthwhile.
They’re more interesting as a character who isn’t doing the right thing.
It’s more satisfying to let them keep being evil.
It makes it more satisfying when they die.
There’s probably more, but you get the idea.
Remember, redemption is when someone realizes they are wrong, and takes steps to doing the right thing. That is not something that can be “deserved,” it is not something that hinges on forgiveness, and it is not something that it is ever too late for! …Unless the person is dead or something.
