Not really darknet when there are searchengines for it is it? Like a kid telling her secret to everyone and still considering it a secret.
No, most of these work by entering the deep Web through forms that query databases and web services for information. Typed queries open up dynamic but short lived results which cannot be
indexed by normal search engines.
Each of these search engines have certain amount of databases indexed some even have data indexed only from one or two countrys. And etc.