Because WN's highest fare is $299, one way. WN gives you a choice of what fare you want to buy on the web site. There are about 6 options with varying limitations. Try that with other airline sites. With their high frequency of flights to most cities if they did not do this, most would buy the late at night $79 fare and fly at noon. Usually the fare differnce is less than $100, most of the time more like $20.