but I've been nice to you for 2 months now, why are you still leaving me
Yes, I had this too - as well as, "But if I shouldn't do all the things you say, how am I supposed to get you to do what I want?" It was kind of funny, as well as astounding!
I think it runs deeper than conscious thought, because it stems from their beliefs. They believe that they are more important than you. It might not be socially acceptable to admit it, but they think everyone believes it regardless.
I've heard it described this way: how an abuser sees their partner's importance relative to their own is like you might treat a pet. You might love the pet, enjoy its company and so on, but it's still a pet. You don't let it eat food from the table. It has to know its place and you might have to shout or behave in ways you'd rather not, if it misbehaves.
Do they think they're doing something wrong? Often not. They're just doing what they need to to get things back how they "should be."
Actually, it's precisely because it's a belief (and not a series of conscious decisions, say) that the only way to end the abuse is to leave the relationship.