It's the Hardy Boys fault.
Or rather, the company behind it, the Stratemeyer Syndicate. Over a 100 years ago, they decided to start deliberately courting children as customers by creating series tailored for them.
For decades, libraries refused to carry any Syndicate books, notoriously considering them to be unworthy trash. Series books were considered to “cause ‘mental laziness,’ induce a ‘fatal sluggishness,’ and ‘intellectual torpor.'" Series books were considered to ruin a child’s chances for gaining an appreciation of good literature (subsequent studies have proven this not to be the case), and to undermine respect for authority: “’much of the contempt for social conventions ... is due to the reading of this poisonous sort of fiction.’
So instead, they forced children to read books that adult liked. But as you say, sort of backfired