“F. Scott Fitzgerald’s third novel, “The Great Gatsby,” is published to mixed reviews and disappointing sales—fewer than 25,000 copies by the author’s death in 1940. By the 2010s, it is routinely selling 500,000 copies a year.”
https://www.history.com/this-day-in-history/april-10
I bet most of those sales are to high school students. LOL
Not because it was good but because high schools and colleges made people read it.