Sorry, yes I was speaking of the Wanna Get Away flight. We have traveled this same week in past years and never paid the amount they have out now. Thanks for the detailed explanation, that all makes sense.
There's a misconception among some airline ticket buyers that airlines release flights with a consistent percentage of seats in each fare bucket -- such as 25% at the cheapest discount fare, 50% at a higher fare, and 25% at the highest far.
Therefore, the thinking goes, if there are no Wanna Get Away fares of Southwest (or no booking code "O" fares on American) on a given flight they must have all been snapped up when the flight was released.
In reality, on some flights, there are no cheap seats (or very few). The airline knows that there will be enough demand between now and when the flight leaves to sell most or all seats at higher fares. On other flights, the majority of seats may be in the cheapest fare class.
I know this thread is about Southwest, but American often offers its cheapest fare only on early, early morning flight, and late, late evening flights. Price sensitive customers are driven to fill what might otherwise be empty seats on these awkward, sleep-depriving flights. Meanwhile, other flights cost more.
Southwest also uses pricing to drive price-sensitive customers to flights with lower demand.