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: 
Why not show them? The data is there, and on the first dozens of pages it's still pretty relevant. In terms of UI it doesn't cost you anything because you're using the same paging control that lets the users navigate through the first pages. If you tell your users that you've got millions of results but you only let them view a hundred, it makes them wonder why. For an "arbitrary" cut-off, 100 pages is very reasonable, while 10 or 20 is a bit strange.
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.