I think it is the exam, Drifter. I teach General Navigation and Flight Planning, and offer private tuition. I have had more people wishing to study Gen Nav on their last chance to pick up a pass, i.e. 4th attempt or 6th sitting, than all our other instructors have in their subjects combined. I haven't had any in that position for Flight Planning, I don't think. I certainly am by far the busiest in the school for private tuition (students from all the schools, I hasten to add - it is not me failing to teach the course!).
That all suggests that pople who are passing other subjects are not passing General Navigation.