Maybe one step removed, if I understand it right, the spam sites make money by offering ad space and traffic, and Google makes money by selling ad placement on those sites, so actually Google and Dark Google are on the same side of the marketplace.

In a way, it's the other way around, Google is paying the spammers for providing billboard space for their ad placement services.

The pervese incentive is that the harder it is to find what I'm looking for, the more ads I get served, hence all ad supported products trend towards becoming useless (see also: Amazon.com)