Oh, I didn't mean at all that people stopped writing first-stories. Those always seem to be the most popular. Just that in the early days you pretty much have to explain how you see the characters and how they get together and why (unless you're just not that good a writer, of course), whereas later, when there have already been 50 stories with something close to your take on their personalities and them getting together pretty much how you envisage them getting together, you are free to assume your intended audience will be able to figure out for themselves where your story fits into the (shipper) fannish consensus and so devote yourself to writing other things. Of course, that does limit your audience to people interested enough in the ship to read it widely.