Lovecraft circle member Everett McNeil, giving good advice in The Student Writer for March 1923.

One can almost hear an echo of his voice at a meeting of the Kalems…

Don’t be deceived by the editorial howl for original plots. Editors don’t want original plots, and authors could not supply them if they did. The last of the strictly original plots was used centuries ago. Even Shakespeare did not create an original plot. An editor would shy violently at sight of an honest-to-goodness original plot. It would be something he had never seen before, something that no magazine, at least in his generation, had tried out.

To which we might imagine Lovecraft pushing back with a comment on new modern ways of telling the story, at least, and musing “Hmmm… The Call of Cthulhu…”.

McNeil may also give us a hint of why he was paid such low rates for a book…

The [book royalty] payments may be scattered over all the years of the copyright, fifty-six in all.

Though that still does not explain why an elderly (elderly, by the expectancy of the 1920s) professional writer would settle for terms that would outlast him by some forty years.