The Decline of Literary Horror
The first one's a short version, the second a scholarly article on it.
The short essay argues that it boils down to a phenomenon I have been able to observe on my own: horror literature apes horror films. This often results in atrocious writing, because what's scarier or evocative on film (e.g. graphic violence) isn't necessarily what's scary on the page (where descriptions of graphic violence can often be clinical, detached, sort of blah). So, with blockbuster horror movies in the 70s, horror lit tried to jump on the bandwagon, it got taken over by a bunch of hacks churning out stuff for the higher demand, then a lot of it disappeared.
The longer, more scholarly essay looks at the loss of midlist authors that occurred during the decline, overall economic downturn, and over-exploitation of the genre (including the possibility that horror is not a genre at all, which I've been wondering since I started).
So I guess I'm laboring in a much smaller market, and it's been fine so far, for my meager plans and desires.