Reddit's search has always been terrible.
site:reddit.com or site:reddit.com/r/nichesubreddit <query> is how I actually find things. Lately I actually have begun to cache important things locally, but I wouldn't assume anyone else is doing that for the particular topics or niche subsection of a topic that I'm looking up.
While I don't doubt that's the case, it's incredibly difficult to get at old content due to Reddit's horrible search experience. I never look up anything old there.