As a kid in the target age range, I bailed after the second or third time Harry gained and lost a positive father figure. There were mounting little issues and the longer the books got, the less rewarding the payoff got. But even I assumed that setting up normalized slavery in your world would lead into a story line that denounces it. Instead, JK didn’t address it in a positive manner and we ended up with HP Adults writing essays defending House Elf Slavery.