Here’s a fun little data point -

I booked a RT in the lowest fare class (non-refundable) and cancelled a couple hours later because I was thinking of changing the outbound flight. Now even two days later the fare class has not returned even though none of the seats have been sold! I assume they only sell one non-refundable seat per flight but still the option has completely gone. So if I want to buy the same ticket it’s an extra $10k. lol. Not sure if this is because of the addition of the new fare classes and if it is intentional somehow or what but it is kind of ridiculous.