It's something we've discussed and voted on a few times over the years, though I suppose it's been a while.
One of the older issues was picking out story posts from the topic list. Not so big a deal with this "Fic Related" forum here, but scanning for topics with 0 replies used to be the main way that some FoLCs would find stories.
Another (more relevant) concern was that FDK posts would put story parts out of order. Late comments (always welcomed!) could bump part 17 to the top of the forum while Part 19 got left behind. It could get a little confusing.
Then there's the fact that some readers prefer the "cleaner" look of the current system. You open the post, and you get just the story, without any distractions.
Don't forget scroll length, either. When you open the thread, you get a good idea of just how long a read you're in for. If you only have a few minutes, you know to save the long post for later. If you're looking to settle in for a nice long chunk of story, you don't have to worry that you'll get 1/3 of the way down the page only to discover that the rest is all comments and discussion.
Oh, and there are some FoLCs who are (or were) in the habit of saving local copies to read offline. Copy the thread and stitch the story together. Much easier if you don't have comments in the way.
So... that's been the system. And it seems to work well. Now I suppose we're all just used to it.
