From Aaron Wall at SEObook:
Consensus bias is set to an absurdly high level to block out competition, slow innovation, and make the search ecosystem easier to police. This acts as a tax on newer and lesser-known players and a subsidy toward larger players.
Eventually that subsidy would be a problem to Google if the algorithm was the only thing that matters, however if the entire result set itself can be displaced then that subsidy doesn’t really matter, as it can be retracted overnight.
Whenever Google has a competing offering ready, they put it up top even if they are embarrassed by it and 100% certain it is a vastly inferior option to other options in the marketplace.
The whole post is (as usual) an excellent read.