I think Raven's point was "Why the books failed," not "Why Martin and Stan were such lazy dogs."

Consider that just a couple of years later, DC had fine success with the re-launches/revitalizations of THEIR super-hero characters by doing the sorts of longer stories and more graphically vibrant and superhero-like covers that Raven suggests would have been a good idea. One can imagine that if Marvel had put the same effort into their product, they might have sold more comics too!

Putting out super-hero comic-covers with stylings similar to Horror and Crime comics doesn't make a whole lot of marketing sense.