Originally Posted by Ber2dca

Those cases present a disruption of service which can only be justified in certain extraordinary circumstances. A passenger who booked JFK-LHR-DUB getting off at LHR does not present any sort of service disruption and indeed any financial loss on part of the airline is purely of the potential, speculative sort rather than an actual loss (i.e. they "could" maybe have sold that seat at a higher rate to someone else but it could just as well have stayed empty).