Mainstream - "Literary" - writers who try to write genre fiction, to make some quick money.
Julian Barnes (as Dan Kavanagh): Duffy, a piss-poor private eye novel. So bad that I can't read his "serious" books: if he can't manage an easy private eye book, his literature, which is supposed to be harder, must be terrible.
Maureen Duffy (as C M Cayer): Scarborough Fear. I quite like what M Duffy I've read, but this is terrible - a horror novel (about Kelpies) which is just irritating - no atmosphere, or believability, either in the characters or the supernatural stuff. I got to about two pages from the end, and then (like the Long Distance Runner) stopped.
Caroline Blackwood: The Fate of Mary Rose. A kind of Ruth Rendell/Barbara Vine plot, but incredibly stiffly written. Also not believable, in story or character.
Literary writers seem to think that genre fiction is really easy - well, it looks easy - and imagine that, with them being proper writers and all, they will be able to do it without really trying. They can't.
Norman Mailer was once going to write a science fiction book. He read some science fiction to see what it was like, and realised that it was far beyond anything he could do. So he gave up the idea. That's a real writer.
Kingsley Amis and Anthony Burgess are literary writers who have written genre books; but the difference is, they put as much into their genre works as they put into their regular stuff; just because it's SF or a Ghost story (The Green Man is one of Amis's best) does not mean that you can slacken off.
Another interesting crossover is when journalists change career to fiction writing. Some of them seem to do very well .. thinking Hemingway and Tom Wolfe.
Others I've read and enjoyed are John Camp, Pulitzer prise winning journalist who writes crime thrillers (Prey series) as John Sandford, and Jeffery Deaver who writes the Lincoln Rhyme chiller thrillers (The Bone Collector, etc.) and is under contract to write the next James Bond novel. Both these guys are very good writers and their page-turners are a pleasure to read.
It's surprising the change works so well because journalism is far different from fiction writing.