Prior to the 1970s, short fiction was the favored form of science fiction. Collected in magazine, these short stories were edited by a revolving door of writers turned editors, such as Campbell, Pohl, and Bova. With Campbell as a notable exception, these editors would return to writing afterwards. It also meant that the body of science fiction was building off of or reacting against a tradition of science fiction established during the pulps. Even as the actual pulps vanished, science fiction writers from Bester and Moorcock to Farmer and Zelazny continued to work with characters and ideas from the pulp age.
However, in the 1970s, short fiction was replaced by the novel as the dominant medium. But instead of the writers and magazine editors shifting over into the book editors slots, a new generation of editors took over that had:
"little reading background in science fiction prior to their assumption of their posts, none of them have ever written it. (The central editors of previous decades were all writers or people who had at least attempted to write in the field.) They have a scant background in the field and for many of them (again, not all) science fiction editing is a way station, an apprentice position on the way to editing something, anything, other than science fiction."
Malzberg, Barry N.. Breakfast in the Ruins (Kindle Locations 2967-2970). Baen Books. Kindle Edition.
These were the editors of which as early as 1968 jokes were made that they thought the genre was invented by Harlan Ellison, a criticism that would continue to be made in 1981:
(to most contemporary science fiction editors "modern" science fiction began with Harlan Ellison, and they have only the most superficial acquaintance with the work of the forties, fifties, and even nineteen-sixties)
Malzberg, Barry N.. Breakfast in the Ruins (Kindle Locations 2979-2980). Baen Books. Kindle Edition.
Because of this, the book editors tended "to publish what looks like science fiction" as opposed to what was truly science fiction. And, since they were risk adverse, or, at the very least, fearful of making mistakes, there was a great narrowing of the field, rendering it a "minor subdivision of Pillage & Homogenize, Inc., presided over in almost all cases by the same group of people." (Malzberg)
"Most science fiction editors seem mostly to seek the assurance that they are doing nothing wrong and since I cannot grant them this assurance I stay away from most of them."
Samuel R. Delany, The Jewel-Hinged Jaw: Notes of the Language of Science Fiction.
This shift in gatekeepers from fans and writers to ticket-punching careerists gutted science fiction of its pulp and Campbell traditions, a loss apparent to the old hands as early as 1981. By publishing what looked liked science fiction instead of the previous mainstream of science fiction, they were no different than the cargo cultists of World War 2. And the readers who were served imitation science fiction instead of the real deal left in droves.