The novel has been replaced.
I exaggerate maybe, but the few novels which get published, including those which receive critical acclaim, are hardly read. A best seller might expect a readership of say; 200,000. A black and white classic film, recycled on a wet Sunday afternoon on the BBC, might measure it's audience in millions.
The novel does just survive, as a kind of marketing tool for the film industry. "The film of the book", we are told and not always truthfully, because they know, after all, that we don't really care about the book.
Since novelists are better known than novels, an association of a particular film, with a particular author is more useful as film promotion, than an association with the book itself. I, for one, have never read a Stephen King novel, but I more or less know what to expect, from a film bearing his name.
A movie is unlikely to follow a novelist's plot, let alone the texture, or even the meaning of the work. (And neither should it, of course.) Coppola's film of Dracula sets itself apart from other Dracula's by calling itself, "Bram Stoker's Dracula". Bram Stoker is no longer a best-selling author and is hardly well known, (if he ever was), but we are invited to think that this particular Dracula has some classy literary credentials, and furthermore, that it is faithful to the book. (I, for one, was fooled.)
The novelist sells a film by default. Ian Fleming is no longer with us, but Ian Fleming's James Bond is alive and well-shaken and re-stirred, again and again.
The merit of a novelist is not here, at issue; there are good and bad novels, but there are few relevant novels.
Enlightened story tellers are now called screenwriters, and screenwriters do not have the last word.
We are grateful for the notable exceptions, the nuggets of cinema culture: the inimitable Woody Allen maybe, though one doubts if his "auteur" status would stand, were he merely a writer. Other artful survivors like Robert Altman, and Martin Scorcese are of course not writers per se. Credit is more likely to be given to a worthy director than to a brilliant writer.
As the novel declines, the language of the novelist evolves, in terms of the influence of the film culture.
Novels are often written commercially, with cinema adaptation in mind, but even obscure novels, with no such ambition, are measured against the evolving cinematic language, and the evolution is out of their control, forever.