Problem: commercial partners do not want their content to be negatively associated with adult content. In the context of Suggested Tiles, this means no sponsored or affiliate tiles should appear within same browser viewport. As an example, MGM would not want a 007 DVD release to be appearing within the same page (in particular, directly next to) where PirateBay tile appears.
It's not a block on these sites, it's there to prevent porn and piracy sites from showing up in the "suggested" page that every privacy conscious user already turned off completely.