I'm also... not sure they understand, like, the basic structure of a "hero's journey". If Harry keeps relying on the adults in his life, or worshiping the memory of his parents, his own ultimate victory is less poignant. For the first few books, the memory of Harry's parents is treated as "sacred" because he's a child and he needs someone to look up to. He's got his parents' memory, Sirius, Lupin, Dumbledore, et al. As the story progresses, all these mentors have to either be proved fallible or die, because if Harry has someone or something to lean on all the way up to the end, the conclusion isn't satisfying to the reader. Harry's parents are both held up as these shining ideals in the beginning, and then that has to be disproved, or Harry just seems like some weird idol-worshipper with Mommy/Daddy issues and no one will care.