My first idea of why not this is that (taking into account I'm mostly a reader too, and when I edit is not podfic pages at all) the editor may not want to write a page about the ff. Not because the ff is bad or anything (or they hate it, or they want to claim the podfic has priority) but because there's something they want to say about the podfic and there's nothing they want to say about the fanfic. One could come up with a template minimum phrase which to use in both cases (idk, 'The fanfic was written by AUTHOR and posted first at ARCHIVE/LJACCOUNT/FORUM / The podfic was read by PODFICREADER and hosted/posted at PODFICARCHIVE/AO3/LJACCOUNT.), but it strikes me as unnecessary every time (though it could be the answer to some cases, of course).