People get in there by submitting a site about gambling that has no links out. Then, after a time, they sneek in and add links. Then they get caught and thrown out, or they put the links up and take them down and so on and so on hoping to escape detection for as long as possible.
Some people have it down to an art.
Personally, I don’t really think it’s worth the effort, but then I have never tried to succeed in this. My experience with them when it was still possible to place these ads wasn’t all that encouraging.