They don't care, at least that is the conclusion I've reached after repeatedly reporting content farms. I think they drive engagement anyway so it's good for business at the end of day. I did not do a thorough study like you apparently did, but anecdotally from the popular subreddits, I've spent enough time on Reddit (unfortunately) to recognize rehashed content that's reposted periodically to 'mine' karma. At some point, Reddit will be just a bunch of spam bots talking to each other and upvoting each other's content while humans will be spectators, or their content will be buried. Either way, this will be great for Reddit as it's good for business (ad impressions). It will be bad for Google as they're training their AIs based off spam and they will notice..