Sometimes airlines offer a super cheap fare as the plane has filled up and there may only be undesirable seats left....none together, and/or only middles. Sometimes they will sell a cheap fare when there are no seats left to be assigned at all. Better to get at least some $$$ rather than let a plane go out with empty seats. The airlines do a pretty good job of figuring us out, and figuring out exactly how many seats to sell at what price (and how many passengers they can overbook by, lol). The conventional old-school wisdom of last minute tickets costing a lot more isn't always true. I take a lot of last minute flights and see those cheaper fares a lot.