WTF are these sites?

Sometimes I like to press "Next Blog" on the Blogger heading. I run across sites like this one, that seem to be nothing but spam. What are these, and what is their point? Clicking on the profile of the "blogger," if you can even call the person a blogger, takes you the listing of his or her other blogs, all in a similar vein. I knew there were spam comments and spam trackbacks, and even good old spam emails, but spam blogs???