Been thinking some more about the whole business of controlling who links to your fiction, and in what ways, and I think this may be one of those things that has a lot to do with who you’re writing for.
But if I’m understanding right, many fanfiction writers are not writing for the public at large, but for a very specific audience: a bounded community with a members who mostly know each other (though also room for newcomers), who have voluntarily set standards for themselves. Someone outside the fandom simply isn’t part of the audience; and someone within the fandom, by becoming part of that fandom, has agreed to its rules.
Put more simply, with fanfiction one can talk about control and have this make sense, because one is dealing with a specific, well-defined community rather than a larger, less well-defined, more public one.