All airlines have tiered pricing. The cheapest seats go first. As more and more seats sell, only the more expensive seats are left.
Try buying a cheap seat at the last minute on any airlines. You’ll likely wind up paying full fare. In some cases only First Class is available.
Someone who doesn’t know jack about airlines wrote this crud.
You got it!
That is why when playing any trip that requires a plane flight, that is why you plan ahead because of cost. You have to.