Have you ever thought of that?

I never have bought any, but the principle is simple. If someone joins without using a referral link, they are not referred to anyone. The site can make money buy matching them up with someone else. Of course, only a tiny fraction of the members of any site are active, so buying referrals is no guarentee that your earnings will go up at all, you may be lucky and get an active member, but you might also get someone who visited once and never came back!

I have heard that you can buy referrals for some sites. Alot of sites do not sell referrals though. the sites that sell referrals, are the sites who will sell an ID of a person who joined the site without joining under someone else. Those people are not referred by anyone and can be added to your very own downline. The site will place that person under you. I have bought referrals before but alot of people are not active so it was a waist of my money and time.