LHR-HKG is about 13 hrs flt time ie ultra long haul and so heavy crew...duty time is in the vicinity of 15 hours. To stop off enroute is out of the question due duty constraints on multi sector flight. Crew are on reserve in LHR for such circumstances as a turn back. 4 hours would have been adequate time to get all concerned briefed and ready for a quick turn around. Max landing weight considerations with a belly full of fuel all come into play.
Last but not least is company policy as indicated by Capt Undies.
There is always more to the situation that that seen at first glance by a number of respondants to this forum.....aka Tan...you miss the point.
All in all a sensible and professional result.