I noticed this years ago, that If you look at the language used by the reviewers you can see that they are usually done by children and teenagers. The reviews usually happen during school months, and large blocks of them happen within a few days. It seems like teachers are having students review books online as part of a class project. Most of these books are required reading in many schools. The typical "This book was boring" post is common when you force today's kids with zero attention span to read something that doesn't' involved robots or anime.