Originally Posted by brunos

I do not understand some of the posts here.
Most airlines have a no-show fee that is separate from a change fee.
To me that makes a lot of economic sense.
Whether it is clearly stated in this case is another issue.
You should not bother about it if you drop the ticket (like the last segment of an itinerary). But if you need to use the ticket, then you have to pay it.

You checked in and did not show at the gate when the flight is closing its door.
In some US domestic flights, it is not uncommon to see waitlisted pax waiting for a seat at the gate.
But for most international flights, that is not feasible.. If you don't show up at the gate, after having checked in, the airline cannot fill your seat. The situation would be very different if you had not checked in, as the check-in counter could have assigned your seat to another waiting pax when check-in closes. This is fairly common at airline rush hours (late afternoon). They could even assign it to waitlisted staff on staff tickets as often the case on longhaul travel.
In specific cases, the flight might be quite empty rather than full, but the no-show fee is fixed whatever the load.

The change fee is a constraint on the the flexibility of the type of ticket you chose. The no-show fee is to insure that an overbooked flight does not leave with empty seats. Even on flexible F tickets there is generally a no-show fee.