Question: There is a study that users do not go past top 3-5 pages in a Google search, on which predominantly everybody would agree. If you would get your best results - it means to be within the top 5 page at least. Merely users abandon to search or change the query if the results do not get laid in the first few pages. In that case, why do we have MORE search results, pages 10, 11, 12, ... and beyond? What meaningful impact does it serve when users rarely do get to that page? Is there any useful content lying far deep?

Answer: 
Search engines such as Google or Bing devote their resources to having high-precision queries for common, precision-oriented information needs. Think of them as recommender systems for popular documents. This works great when you're interested (as many people seem to be) in what Britney Spears is up to, for example.

If, however, a user's information need is recall-oriented, then settling for one of the top few results may not be appropriate. Think about searching for symptoms related to a disease, doing research, or trying to make a new connection between seemingly unrelated concepts. These kinds of searches may require people to dig into the results more deeply.
Users often do not find a good result in the first page - this depends on how specific of a result they are looking for and how many false matches fit their query.

I personally often go through a few pages of search results before refining the search query to try and improve the quality of the results.