A few historical musings....
In the 70s this was often done . LHR-LAX-PHX on TWA was cheaper than LHR-LAX, so many pax bought the longer journey and then just hopped of at LAX.
Then there was even something known as a ‘fictitious one-way back haul’ when for IATA fare calculation purposes the ticket was written more cheaply, as if to travel via a point that was overflown (or even avoided) but never touched down. But that was also in the days when the name of a physical passenger did not need to be checked against individual documentation. As an example, on the Pan Am Lockerbie flight there were a dozen or so students from the American school in London who had swapped tickets with others, causing havoc for those trying to work the manifest for next of kin.
On international sectors where the airline holds traffic rights for A to B, and A to C, but not B to C this can be a boon for non rev employee travellers who want to fly B to C.
Can you imagine if the same thing was done in the retail trade such that if you bought 3 bananas you were required to eat them all, because only eating two and throwing one away was against the terms of shopping at the supermarket?