Villain Standards

Something I've noticed when writing is that villains are the easiest thing to write. This is in part due to how they seem to have lower standards than protagonists, whom always need to be complicated. Paper thin protagonists are frequently more frowned upon than paper thin baddies. In fact I can think of a couple of baddies who are 2D but everyone loves. Notably ones from animated kid shows like Samurai Jack's Aku and Gravity Fall's Bill Cipher are both popular and beloved. One wants to spread chaos, the other wants to retain power. Though Joker is sometimes complex, people usually love iterations of him despite a lack of nuance. A lot of the time they love a good psychotic freak. Whenever there is a semi sympathetic villain out there, people seem to be blown away. Even if it is just "The world wronged me" or "X family member died."

This opens up doors for people to be more creative with villains in my eyes. I'm trying to write villains like protagonists: unique motives, interacts with different individuals in different ways, don't establish evilness each scene, have a character arc, and one thing I don't see enough of is to have insecurities and flaws that other characters help them with.

But this also reminds me: How come flat versions of the Joker and Aku are beloved while other 2D villains are despised? What is the standard for a "good villain" and how much does it very from every part of the story?

(I think one reason is that a conflict is a gap that doesn't need complexity. It could just be a tsunami. Meanwhile a protagonist needs to have their story arc correlate with the main plot)