Last fall, I called Alaska about switching to an earlier flight the following day. I was told that if I wanted to confirm standby, it would cost $25 or I could show up day of flight and standby for free. I chose to show up early to standby without the fee. Since this was 6:45am PDX-OAK, I didn't have a problem getting on the plane but it does make me wonder why airlines do this?

If my original flight was sold out and someone wanted to take that flight, they wouldn't know that I was going to standby for an earlier flight? It would seem to be in the airlines' best interest to get people on an earlier flight that is not sold out to free up seats on later flights in case of last minute purchases or other issues.