Many people enjoy discussing and judging the morals of characters in films, but that’s not the main point. Very few characters are entirely good or entirely evil, which tends to result in dull and poorly made movies. Regardless of whether viewers resonate with the story, they should show compassion for the characters. It’s important to interpret their motives and circumstances to understand what led them to make certain decisions and to reflect on ourselves.
The Joker has a motivation though, his worldview is that everything is chaos and he needs to prove it to everyone else. Especially Batman.
But for the joker motivation adds almost nothing
It means that when he does things, they feel like things the Joker would do. In the Dark Knight he takes all the mob money and burns half of it, because that is a Joker thing to do. Two Face wouldn’t do that, because Two Face has different motivations.
That is the reason to have motivation. It doesn’t need to be complex, just nuanced.