Revealed that villain’s schemes secretly served the greater good, somehow
Villain switches teams out of expedience; protagonists overlook the fact that they’re still a huge jerk because they now benefit from it
Context or status quo altered so that villain’s previously harmful actions become constructive and useful with no changes on their part
It turns out that villain wasn’t actually responsible for the one specific thing the protagonists are trying to stop or get revenge for; everything else they clearly did do conveniently ignored
Villain never repents or makes amends for any of the awful stuff they did, but they’re really hot, so no one cares