[Asooka]

Rather, allow people to buy "don't-kick-me" tickets for a bigger price and once the plane has been filled with don't-kick-mes, notify all other ticket holders that they're being bumped to a later flight. If any don't-kick-mes don't show, the waste is covered by the increased price.

[exclusiv]

But there is really no waste when they sell out 100% of the seats. If people no-show the seat is paid for.

The airlines are trying to make it sounds like they are just trying to reach 100% capacity but in reality they are trying to arbitrage the fact that a few people buy non-refundable tickets and don't show up.