This villain is easily shipable because they’re so incompetent, stupid, relatable, or sympathetic that they’re not really a genuine threat to the heroes regardless of how evil their intentions or motivations. Because the Anti-Villain tends to lack many traditional villainous traits, they have a high chance of redemption, and as such, frequently end up becoming late game teammates to the heroes, which increases their chance of creating romantic or sexual tension with a hero that can actually build into something. Similar Anti-Villains like Scorpia from She-Ra and the Princesses of Power, Lotor from Voltron: Legendary Defender (until his contradictory and uncharacteristic re-write), and Poison Ivy from Harley Quinn are three villains with sympathetic enough desires and beliefs that the first two end up reforming into good guys by the show’s ending, while Poison Ivy is a villain in name only who keeps insisting she’s not an actual villain. That, paired with him becoming a certifiable hottie in Book 3 cemented Zuko as one of the most shipped characters in Avatar. The audience is allowed to see his struggles, shortcomings, insecurities, and his growth.
However, the story dedicates just as much time to showing his story and his arc as much as the heroes. Zuko from Avatar: the Last Airbender is a perfect example of a villainous foil to protagonist Aang. The Anti-Villain is a character who is on the antagonistic side of a conflict, but is morally and personally a good person.