First, because they're out of date. Most of them were written four years ago and more, and even at my advanced age I find myself changing so much over time that I'm now someone quite different from the person I was in 2001. To me the stories are curios- relics of what life was like in the first flush of a new fandom that was mostly manga-based and isn't at all the fandom that exists now. They have no more relevance for me. I don't mind keeping them up so people can find them if they look, but I'm not going to offer dusty goods for strangers' perusal. Gonou might be the exception; it's been pounced on by enough translators to suggest that in some sense it isn't my own work anymore, but a fannish artifact that belongs to the Saiyuuki fandom as a whole.
But I still don't want it archived. Once my fics are in an archive I have no more control over them; they're where they are and can't be removed without fuss and bother. More, they get presented in whatever form the archivist feels like presenting them, and maybe she'll preserve my italicizing or maybe she won't; and maybe she'll make the text column two inches wide and fill up the rest of the page with her clever html and graphics; and maybe she'll print the story in tiny fonts and purple letters on pink backdrop. A story in my directory looks the way I want it to be seen: black and white and nothing but text, take it or leave it. That isn't the case with other archives I've seen, except the first lamentably defunct one run by Tro.
But the final reason not to archive is the basic one: people might read my stories if they're in an archive, especially one currently being heavily publicized. I don't want to know that strangers are doing that, possibly in numbers greater than one a month. It can be deleterious enough that friends read my fic. Other writers may be different, but I find it hideously difficult to be honest to my own ideas when I know somebody else is going to read what I'm writing. I end up not saying things I might want to say- none of their business or that won't sit well; I add stuff not because it pleases me but because it will please the invisible readers; I write whole stories I wouldn't want to /read/ myself. Having an audience is bad for me; archiving my stories pretty much guarantees me an audience of some kind; and therefore I avoid archiving my stories. QED