In answer to really all of your questions - because early on we trained the surfers to look for free porn - that got them into our filtering mechanisms (hubs, traps etc) and we could find out what they would really buy if it was presented right
As far as why people target it now for keywords - some do it because its a built in traffic source and they love to see the counters go round and round - sorta like asking why someone would do a tgp gallery - some people think their dick is bigger if they have more traffic going through a page
Of course the smart ones figured out a long time ago that doing something that gets way less traffic, but creates more sales, works more efficiently and costs less in overhead
