I'm not sure what advertising they are using. CC tried google ads a while back and so many inappropriate ads came through they had to stop using it. So perhaps the ad is a paid for ad by the company itself and not through google, and that's why it's only the one ad.
Also many people use this site as a hunting grounds for dating, which regularly upsets many users. Perhaps by using such an ad they are hoping to provide people coming here for that purpose an alternative.