...Uh, come the 90s, Bridge to Terabithia was a required reading book that I don't think anyone my age cared about. The popular series I remember were, in no particular order: Animorphs, Goosebumps, Nancy Drew, Harry Potter, and Redwall.
I think it's much simpler, adults don't know what kids are interested in. For example, just before that age I was interested in animals and the solar system. Read anything I could find on them, and had no interest in anything being pushed by school or parents. At age 9, I just happened to see Animorphs #11 The Forgotten in the impulse-buy section of our local drugstore and begged my parents for it - for anyone unaware, the Animorphs covers showed kids turning into animals, which was how it drew my attention. That set me onto sci-fi in general, then fantasy - and I've kept reading since.