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.
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.
Couldn’t two face just be written to have flipped a coin and ending up burning half the money as a result
He flips the coin to decide people’s fate, not to deatroy money.
But you also just gave another example of a character’s nuanced motivation and morals. That is what makes Two Face an interesting character in a different way than the Joker!
A villain that burns the money for no reason other than moving the plot forward would be boring.