Originally Posted by
mahasamatman
It's all about marketing, and the fact that many booking engines still put 1-stop "direct" flights above other 1-stop flights. The markets they want to push get the direct flights.
But why would the booking engines still favor same-flight-number-multiple-segment flights on airlines where that does not guarantee the same plane? All it does is increase the likelihood of angry customers who, for example, booked UA 889 LAX-SFO-PEK under the false belief that it would be the same plane, then misconnected at SFO because the LAX-SFO segment was late and the SFO-PEK segment took off without them.
Some airlines (e.g. WN and AS) do use the same flight number to indicate the same plane continuing on to another destination.