Hello! I am a fandom person who writes and reads LOTS AND LOTS OF PORN. I’m also a fandom person who just closed out of a huge—like, >100k—fanfic epic at the last chapter, which is where the author put the porn. The story was well-written. The porn was well written. So why did I close out?
Because the story was over. It didn’t need the porn. So adding the porn made it a less good story.
This last-scene-sex-scene-close-out thing is a thing that I do, when reading fanfic, a lot, because this thing where the author tacks on sex after the story is over, and it doesn’t fit, and it makes the story worse—is a thing that fannish authors do a lot. And it’s kind of a pet peeve of mine, so I would like to talk about a) why this happens, b) how to spot it in the wild, and c) how to avoid it in your own writing. As always: you do you, and YMMV. Write what you want to write and fuck everyone else (including me!). But this is a very frequent thing that causes many, many, many fanfic authors to lose at least one reader (me), and I suspect more readers as well, so if you want to know how to not do it, read on.