/a/ likes to discuss ongoing shows. That's what the majority of our time is spent doing.
Go back in time 2 or 3 years, and /a/ was talking about Mushishi.
If you want something more, then pose an interesting question or theory other than "/a/ doesn't talk about me" Otherwise, we've already discussed Mushishi. We've already agreed it kicks ass. And since we can't really fap to it (well... maybe we can a little), reposting image dumps of the show every day wouldn't get us anywhere. And you know how much we bitch about reposts.
So for the most part we're just going to stick to ongoing series. Even then, we'll occasionally see a rise in popuarity of older stuff and see some good discussion of it for a few days/weeks. As already mentioned, Aria and YKK have seen a recent rise in popularity of discussion. And I remember a little while ago when Kino threads were appearing with regularity. And before that I remember a time when LotGH was seeing lots of discussion for a brief period. And there are plenty more examples like these (these are just a few of the ones I remember).
But if you want a good Mushishi thread or even threads, MAKE IT FUCKING INTERESTING. Give us something that we don't already all know. Some interesting tidbit of information, or maybe an image dump of rare artwork.
TLDR: If you want to talk about older anime, make it fucking interesting. Otherwise /a/ will stick to discussing current shit.