No room at the top.
What is a search engine supposed to do in order to increase revenues? One of the earlier attempts to find an answer to this question (I dealt with it three years ago) was the portal. The idea behind the portal was that even though the purpose of visiting a search engine (or a catalog) was to get from it to somewhere else that interested you, maybe if the engine offered additional services people would linger longer on the site. This proved successful for some, but it also caused crowding out at the top. In the end only the powerful remained, and those sites, through trying to offer something (or perhaps everything) for everybody, lost whatever individuality and interest that they may previously have had.
It may be the case that only the strong survive as portals, but not all the others fade into oblivion (at least not all and not yet. There are still some non-contenders around, and they still want to get in on the act. So there's always an ongoing search for the niche that's going to provide a sustainable income.
Go to: Seek and Ye Shall Buy.