i suspect it also speaks to a certain optimism that, deep down, people want to have in their storytelling. we want to believe that villainy can either be defeated or reformed, and especially in the case of hero -> villain -> hero we seem to need to believe that our hero has never gone irredeemably bad.

it's odd that, despite it going against what we see so often in the world, we want to believe that compassion and goodness can spring from where there was none before, but we find it so intolerable to think that it can be entirely and lastingly expunged.