The big question is why don’t the damn editors stop them?
Speaking as a freelance editor, I can tell you why.
It’s very, very hard to edit these days. Much harder than it was in the days before self-publishing, because now authors have alternatives. I don’t know how the Big Five react to that, but it scares the shit out of small and medium presses. Publishers are often terrified that writers are going to walk if they feel…unappreciated.
Regrettably, there are a lot of writers who didn’t serve their time in the salt mines of fanfic and who don’t know how to handle having their work proofread or criticized. There’s also a widespread belief that editors are all jealous of the writers that they edit and want to ruin the writers’ work.
(This is one of the silliest beliefs I’ve ever heard, incidentally. Editors want the manuscripts that they edit to be readable, to have a coherent and consistent story, and to become wildly popular and win all the awards. The better the book does, financially and with critics, the better the editor’s position. )
So the editor nowadays is often caught between a publisher who is scared to death that the writer will pull the book if their work is criticized and a writer who has never before been told that anything they write is imperfect.
What the editor has to do, under such circumstances, is figure out what is so flawed that everyone will notice versus what’s flawed but will probably get a pass from readers and critics. Because if you want a writer who isn’t accustomed to criticism to eliminate grotesquely offensive racism or anti-Semitism in a scene or to cut a graphic eight-page rape scene (which has fuck-all to do with the plot), you’re going to have to let some of the flaws stand. Which is why things like the above get passes.
You see, almost no one writes sex scenes well. Almost everyone thinks that they write sex scenes well. And since most people believe that they are writing sex scenes brilliantly (and, nine chances out of ten, are writing what arouses them), anything critical that the editor says will upset the writer, who will feel that their writing and their sexual tastes are all being judged and it’s not fair. And a surprising number of writers will turn Karen on the editor. Only instead of the “let me speak to your manager” line that retail workers hear so often, the writer will either phone or email the publisher about the editor’s criticisms and how dreadful they are and how threatened the writer feels.
And then the publisher will get upset, and they will take the editor to task for…well…proofreading and editing, because the writer is angry and distrustful and just about ready to walk out the door. Publishing houses are businesses, and they can’t afford to outrage the writers.
So instead of critiquing bad sex scenes, most editors will just let them stand, as they are the most personal, in many cases, and are the ones that most writers will fight to include. And in exchange, the editors will get a writer who is more or less willing to rewrite or cut…oh, maybe three or four scenes/errors that are far, far worse.