View from the wing provides a handy piece of information (via Marginal Revolution):

Regardless of what you pay and what fare class you’re booking in, your travel on United between San Francisco and Nagoya, Japan is going to have almost no effect whatsoever on United’s decision-making. They’ve got a very large contract with Toyota and they fill up their 747 with cargo and the flight goes out with very low load factors yet is still profitable for them to operate. That’s why the single easiest flight in the entire United system on which to score an international premium class award ticket on is San Francisco- Nagoya...