I think you also have to remove subreddits that the member is not part of showing up in search results. Several very niche subreddits I participate in have fairly regular low-quality posts by clueless people who just stumbled across them in search (usually looking for something related but different). The bar for searching for a term and posting in the related subreddit is SO MUCH lower than the bar for finding a forum in a web search, signing up for an account, and posting. It might sound minor, but it's not.