I guess I find the question to be off point because when I search for flights from SFO to JFK I am looking for the ticket itself, not a fourth party that can resell the tickets to me. So all the links to Kayak etc are bad results anyway, although direct links to airlines' own sites would be good results. But that's essentially what Google Flights is: a vertical that cuts out middlemen.
If I search "sites that resell airline tickets" then Google Flights does not appear anywhere in the results.