All of revenue manage sounds fishy to the customer. The whole lots of fare classes, advanced purchase requirements and other fare restrictions ARE complicated but are aimed to maximize revenue and seem to work. One explanation I have seen is that cheap seats pay for operating the flight and higher fare classes are mostly profit. Leaving unsold allocated low fare class seats available not only allows for SDC but for people changing return tickets, including dates, and using original purchased fare class for repricing, if available, instead of applying advanced purchase rules for the change.

Not that long ago DL had a rule that award tickets canceled within 72 hours would not get miles credited back. This was in response to people booking multiple award F seats on a flight they were traveling on and canceling the award tix a few hours before departure to increase F seats available for upgrades. People will exploit any loophole they can find. This is a reason to limit SDC so folks don’t buy cheap tix on empty flights and SDC to expensive nearly full flights they really wanted. The airline version of WFBF, you want the expensive flight, buy the expensive flight.