Hosters host the offending content on their equipment. Search engines at least have specific knowledge of the content they direct to, and might have a (partial

Hosters host the offending content on their equipment. Search engines at least have specific knowledge of the content they direct to, and might have a (partial) copy. But registrars don't have any of this. They provide a service that is completely independent from any content being served, and the offending content never touches their infrastructure.