Donald at 2Blowhards analyzes the covers of pulp fiction magazines and notes:
Perhaps the main reason why pulp cover art wasn't especially refined was because pulp editors and art directors (if there were any -- often the editor dealt with art as well as with words) didn't want refinement. What they wanted was eyeballs, and the way to attract the attention of people scanning magazine shelves of news stands was dramatic scenes and bright colors. As a matter of fact, cover artists were often ordered to include areas of bright red because it was thought to be a good attention-getter. Another important factor had to do with the low pay; artists couldn't afford to spend much time on refinement if they expected to make any kind of living painting pulp covers.