I guess it's because everyone used to think that the social aspect will have such a huge impact on search that it will disrupt and replace Google's search model

I guess it's because everyone used to think that the social aspect will have such a huge impact on search that it will disrupt and replace Google's search model. But I think they were wrong. The social aspect is a minor aspect at best regarding search, and it should be just one of Google's hundreds of other search signals, not 50% of the search algorithm.