The reasoning is that some people cancel their reservations, so if you have a good statistic for how often that happens you can overbook to take up the slack and still have a full plane. Airliner margins are pretty thin, so they jump at opportunities to avoid "waste" like this.
Scammy? Ehhh. People get way more than their money back for switching flights, which I consider enough to make it un-scammy. Others might reasonably disagree.
Scammy? Ehhh. People get way more than their money back for switching flights, which I consider enough to make it un-scammy. Others might reasonably disagree.