A huge difference is with no-shows. In the covid era, in theory DL could sell out all 67 seats on a 100-seat plane (middle seats empty) and none of the 67 passengers show up. Remaining passengers who wanted to book this flight at any price were denied as it was sold out. Yet all 67 no-shows would still get a 100% credit towards another future DL flight. Pre-covid DL would get to keep $200 per passenger, and all BE and award ticket fees. This is not sustainable for DL.