Well, the search engine provide the playing field for this BS. However, I believe that the problem is exacerbated by a few programs who are prepared to turn a blind eye to illicit activities and prefer to profit from them rather than building long term relationships.
Getting the spam onto the SERPS and generating big traffic is one thing. Being able to monetize this traffic with the help of unethical affiliate programs makes this a winning proposition for spammers (let´s have a little blackhat SEO contest, shall we?). I can´t reform Google but I sure can put a bit of pressure on the programs that think they can continuously outsmart honest affiliates.