pull down to refresh
The big issue is lack of incentive. Stackers don't get any reward for zapping old content, which means they don't put any effort into finding it and engaging with it.
I think there are some ways to fix this and have stuff recirculate through the hot and top feeds.
That's what the "Random"-list is for, no? There are also some users who've made it their Jam to curate and essentially wrap said posts in a fresh post.
I think this one's not something SN can "fix" per se, but something we'd have to make a conscious decision about on an individual / Community-Level.