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What is the main reason for this usually? I don't think that there is really a main reason for this....   a couple things play in concert.. As with many sites that produce great content  my bet is that... Lots of people have grabbed your stuff and are using it.  They are using your titles and your brand and your words and your images to enrich a site that is monetized with ads or affiliate programs.   Some of these people are really smart about optimization.  Some of them have created sites that have become moderately powerful. Perhaps this has not been theft.  Perhaps you gave your content away and now you are paying the price for creating duplicate content that is being used against you by smart people. And, google says that they are "good at recognizing relevant content to return  to the searcher"... but they have not decided to put the resources into returning the original version - even after we tell them which version it is with rel=author as they requested.  They have simply not decided to put the resources into this- even though I am sure that some of them would like it to work that way. There you have it.