Let’s take a practical example - Toronto to LaGuardia. I pick a random date a ways out - Tue. June 13th; they have their own code names for “cheap, not so cheap, etc.” Every airline will have their own euphemistic names…
A -Economy Tango - $144 (all in northern pesos, not real dollars!)
B - Economy Flex - $281
C - Economy Latitude - $815
D - Business Lowest - $386
E - Business Flexible - $864
(My own letters, not booking codes)
Now seriously, look at that - an economy seat for 7 times the cheapest rate. Nobody buys that unless they really need flexibility.
Only C and E are refundable.
Change a flight - $200 for A,B, D - free for C and E
Change a flight same day - cheaper on the La Guardia flight - $100 normally $150 for A, $75 for B, free for C, D, E
Standby is free for C and E
See a pattern here? The people with a C or E ticket have paid through the nose for the privilege of being able to no-show, select a different flight (or decide to fly earlier) without a penalty - over and over. Rebooking costs as much as the flight originally cost for some others.
So there’s a good chance a decent number of C and E passengers will not show up, or will change their mind within a day or so of the flight. If you can make a good guess how many, you can sell a chance to use those seats to the $144 customers. Plus, you only sell so many $144 seats (to encourage early booking) so people buying a week or less before on a popular flight will pay $281. If the C customer is a no-show, you’ve made an extra $241.
Plus statistics tell you that a certain number of A, B, or E passengers will not appear for assorted reasons - illness, death in family, car broke down, brainless…
If overbooking is disallowed or the penalty becomes too high, then the airlines will simply adopt a different strategy. The most obvious is to raise prices for everyone, or eliminate no-charge ticket changes, or some combination of that.
There’s nothing magical about this - it’s the same as the hotel business. If you don’t rent that room, they you lose that chance at money forever. So if the customer doesn’t show up on time, rent it to someone who’s waiting. We’ve all heard those “sorry but we thought you weren’t arriving” hotel stories. Same idea.