I don't think it's entitlement so much as a lack of curiosity and drive. I'm in no way a prodigy (intelligent, sure, but not beyond normal levels), but went through much of the same in high school. In grade school and middle school, most things were new and interesting, so I was almost always engaged in what I was doing and did very well. In high school, I attempted to push myself by taking honors classes or higher level classes. I quickly found out that for history and literature, I just flat out didn't care, and my grades in those classes suffered as a result. It wasn't because the material was tough, because it wasn't; I was just more inclined to actually do the work for my math and science classes. When I dropped back down to the normal level of history and literature, I was still bored, but could largely ignore the classes and still get decent grades. In my senior year of high school, I simply became bored with everything, and just skated by. It was never because the work was too difficult; it was always because it was boring and I just didn't want to do it. Fast forward to college, and things were new and interesting again. I excelled at the classes because I was learning new things, and things I wanted to learn.
The point is, someone can be the most intelligent person in the world, but if they have no drive or don't want to achieve greatness, no amount of pushing and prodding is going make them do so.