[Cthulhu_]

Because Google earns more money off of those results than legitimate pages. That's what I think anyway. Some years ago they said they were going to crack down on SEO spam, content farms, even website popups like newsletter subscriptions, asking people to report them through a browser plugin.

But since then... nothing, and the content farms are prominent again. Google doesn't care because the competition isn't significantly better, and they don't actually care about the search results, they care about ad impressions which they will get regardless of how people end up on pages - or what pages for that matter.