Very interesting. Remember that in 1940 comic books, as we know them, were only 2 or 3 yeas old. Before 1937, most comics were reprints of new paper strips. Modern super heroes began in 1938 with the birth of Superman and Batman. There were also more and more non-super hero comics, but of other genres that before now were mainly the realms of pulps.
Before comics, the popular culture of fiction at the time were pulp magazines. These were magazines printed on crap paper and varied in length. Some had an anthology of short stories, others were full length, albeit shortish, novels running 50,000 words or so. They were seen as cheap entertainment. Sort of looked down upon. Many people hoped to hone their craft in pulps and later write "real" books. Comics were even lower in the pecking order and were so for a very long time (Fun fact, Stan Lee's real name was Stanley Martin Lieber. In 1941 he used a pen name, Stan Lee, saving his real name hopefully for "real" literature in the future.)
The first pulp showed up in the very late 1800s, but were super popular up until WWII when the paper shortage had a serious effect. Some classic sci-fi and fantasy authors got their starts in pulps or had some of their stories first published there, such as HG Wells, Lovecraft, Asimov, Edgar Rice Burroughs, and one of my faves, Fritz Leiber.
The 20s and 30s were when they were most popular, with Science Fiction, western, adventure, detective, fantasy, and romance all being staples of the genre. In the early 30s also came the rise of "character" driven stories. These had some popularity in the early 1900s, but they had a resurgence starting with The Shadow in 1931 (inspired by the menacing narrator of the radio program "Detective Story Hour"). Many more were featured in the various anthology stories. While many of these pulp heroes are lost to obscurity, many of them you are hopefully familiar with: The Shadow, Doc Savage, Conan, Tarzan, Zorro, Buck Rodger, The Phantom, and more.
And even if you are unfamiliar with these character, you know their offspring. Most notably both Superman and Batman "borrowed" heavily from The Shadow and Doc Savage.