In Apocalypse World, motivations are clear. There is resource scarcity, and you got people trying to kill you, and you need to stake out a place in the world. Easy.
And if you're one of those classes that Vincent warns you won't have a constant instream of motivations, you still got that, 24/7. Some classes even have more motivation on top of that, like managing your town or leading your batshit-crazy cultists around.
Monsterhearts poses a new challenge, here. There is no material scarcity. While there is the threat of monstrous attack and weird violence, I imagine it being less immediate of a threat (unless you have your emotions at stake, which should happen all the time, if you're doing it right).
So, what is that motivation? What stops everyone from just accepting one another and having emotionally-validating sex with one another? What makes this a heartbreaking tragedy, in the most teenaged of senses?
I think that part of this comes into play when you look at the guiding principles, and how they drive situation. If the principles include Acceptance is Never 100% right at the top of the list, you've got a lot of the motivation right there.