I agree that revenues are way down. Remember when people thought porn+internet was a license to print money? Those days are long over. When the marginal cost of a porn pageview approaches zero, the amount you can charge for that pageview approaches zero. I believe the majority of porn sites don’t make any money, but they don’t cost much either.
Waitaminnit…there’s FREE porn on the internet?
Tangentially related, I guess, but what’s the deal with sites that beget new sites, sometimes 3 or 4 at once, when you try to close them? I’m not necessarily talking about porn sites, although when this occurs, in my experience, you’re ultimately brought to porn sites whether you intended it or not.
My question is what’s the point? So I click on a link on an admittedly dodgy page out of curiosity, and suddenly have 8 (or whatever the number is) loud, gaudy, and trashy porn pages up on my screen, blinking and flashing away, right? Now, perhaps I haven’t investigated closely enough, but I don’t see sign-up prompts, offers of memberships, requests for cash, or anything like that; just pages of thumbnails which, upon clicking, opens yet other pages of thumbnails. What am I missing?
The person running the Hell-page has advertising deals with someone-or-other (possibly porn pages) to get paid every time one of the payer’s ads show up. If the Hell-page can make 500 windows pop up when you click a link, the Hell-webmaster gets paid 500 times. I think advertisers have mostly caught on to this now, though, so it doesn’t really work any more.
Someone mentioned that the sites are cheap to run. I don’t think that is true. The bandwidth on some of the tube sites must be horrendous.
“Free” and “good” aren’t synonyms. 
I remember there was a movement a few years ago to make mini-monopolies. The model would be exclusive to one site, and the only way to see this model in action was to sign up with that site. I doubt it lasted, but it was a good idea at the time.