Andrew Liptak, writing about the rise of the paperback, for Kirkus:

Technological innovations helped as well. Silverman explains that “in the new century, the opportunity for mass-market paperback books emerged again as a result of the introduction of the high-speed roll-fed printing press.” This allowed publishers to print books far more cheaply than ever before, and combined with their distribution methods, Pocket Books was a success. Davis recounted that the publisher’s new books “practically sold themselves. Aided by an enthusiastic reception in newspapers and magazines across the country, de Graff and company did not have to go to the mountain because the mountain was coming to them.” The major publisher’s perception that their products were only valued by the wealthy was a self-fulfilling idea: The masses didn’t buy hardcover books, while the wealthy did. However, hardcovers were expensive and out of reach for most Americans, especially at the end of the Great Depression, and thus only available to those with money. Pulp magazines, a refuge for science-fiction stories, which were bought in larger quantities by the poor and middle classes in America, were largely thought to be of lesser quality, in terms of the physical book, but also that of the content. Now, with an outlet for cheap books, the American public came out in droves to purchase them.

You might say we’re seeing something similar today, with ebooks.