For starters, the reason these sites are so popular is because they prey on our greed, as the majority of the content they advertise is illegal in nature (i.e. movies, music, and software). So, along comes a newbie to the piracy scene who sees this site has pretty much everything s/he wants for a price that's too good to be true and he takes the bait. Almost without exception, these sites offer a "limited time" deep discount offer, which at first seems like an incredible deal (i.e. $4.87 instead of $39.87). More often than not, however, included in this is a mandatory sign-up for a "3 day trial membership" at a partner site, which is often porn. A lot of this happens behind the scenes, so you don't even know until you get your credit card bill (or until your wife is screaming to know why there's a charge to "FREEXXXPASSES.COM" - whichever comes first).
So what happens next?
Well, with your credit card details safely in their hands, you quickly start to realize that they DON'T actually have ANY of that amazing content they claimed to have. In fact, they have nothing at all - and you've just been SCAMMED!
Often what happens is they send you a login/password that doesn't work. So, you start digging around for answers on the site only to find that the support sections are always INSIDE the members area - an area you can't enter because you can't login! This evil - albeit ingenious - Catch-22 type of trick is intended to get you to forget the whole affair. After all, you only lost $4, right?! WRONG. You were actually charged anywhere from $40 to $100 USD, depending on the site you signed up for and how many extra option boxes you "forgot" to uncheck. Check your credit card statement, I couldn't believe my eyes.
If, in the odd chance you do get a login/password that actually works, you'll either be going in circles on their pages, directed to download legitimate programs like Limewire, or forced to download some program onto your computer that will just rape it with spyware and/or viruses.
Yep, no matter how you look at it, it's theft and fraud, pure and simple. Nevertheless, it makes them ridiculous sums of money. Looking at the alexa.com web-ranking for some of these sites, you can see that some of them are way up there, meaning that they are likely getting TENS OF THOUSANDS of visitors per day! Now let's say that just 1000 of those sign up and the scammers manage to STEAL at least $60 from each person. Woah, that's some serious coin they've just made, all at our expense. They're sunbathing somewhere in the Bahamas on their private yachts, living the life, while we're fighting to get $60 back. Bullshit, if you ask me!