Now, we can argue that Disney expects to make up that loss in food and merchandise sales but it appears that this just isn't happening. I think we would be naive to believe that Disney doesn't track how much it costs them to service every guest in the park, regardless of if that guest paid full admission or not. The very presence of a person in the park costs Disney money and if that guest isn't spending enough on food and merchandise to offset that cost then it's a loss.
It seems safe to assume that the admission price covers the cost to service that guest during a full day at the park. This assumption would then lead me to believe that everything that guest spends in the park is mostly profit. However, with the APer Disney not only has to account for the initial cost of servicing that guest but then they have to find a way to make a profit off that guest. Like christianAdam already stated, it just doesn't seem to be happening and the entire concept is upside down.