"The Sweet Spot"
Gish Jen’s article “Why Do People Love ‘Catcher in the Rye’?” is interesting on a number of levels. But the literal question asked by the headline seems not-so-hard to answer—the book is perfectly pitched at the sensibilities of high school students, i.e. people old enough to read real books but not yet old enough that nobody can force them to read literary fiction.
Once you exit high school the universe of “people” who read novels just starts to shrink incredibly rapidly.