People on Reddit upvote and downvote comments all the time. You cannot upvote or downvote a Google search result. Unlike SEO spam surfaced by Google that only needs to satisfy Google's ranking algorithm, SEO spam on Reddit needs to do that and garner enough upvotes by a diversity of users. Even though some of the users might be sock puppets or bots, the value is still there as long as there are more humans than bots.