That is quite a detour.

That's almost a quarter more distance, hours more flight time, needs an A340, can't be done with the current schedule i.e. would need to rework the slots and equipment rotation etc. etc.

In other works it would hardly be a realistic and profitable option, especially since passengers would have to be inconvenienced anyway because of a new schedule, might as well just reroute them / move them to the other HKG flight.