To a certain extent it's a battle between advance and retreat. Sure, what we'd like to find again was interesting. We probably have fond memories of it. But if it's something that we can't remember immediately, chances are good that it's not something that it's worth investing the effort finding again. While we're searching for it, after all, enormous quantities of new information are vying for our attention, and taking the time to look for something from the past means not being exposed to something at least as interesting from the present.