It's true that if you are a true frequent flyer, it's better to stick with one airline, especially for U.S. domestic routes. Suppose you take 100 flights per year, and are at the top tier elite level of the airline, and you get free upgrade 50% of the time, that's the reward for your loyalty to this airlines. But if you fly 10 times a year domestically, I just don't see the point of being loyal to any airlines.