The reason for reversal might be as in your case, elective. It might be denied boarding on the airlines part for whatever reason.
How often do I need to explain - it wasn't elective on my part - my flight was CANCELLED.
If my flight had been delayed, I would agree with you that it was elective that I chose not to wait for the delayed flight. But in this case my flight was CANCELLED, and I was given a full refund.
I could have chosen to accept the offer of an alternative flight, but as my booked flight had been cancelled I was equally entitled to accept the refund and leave the terminal.
The issue is whether BAA and/or the airline are then entitled to hold the passenger airside at their own convenience, which is what happened to me.