I'm guessing that if the aircraft had a fault, it would not be able (within regulations) to take off again without engineering work, so continuing as far as possible and diverting in China would have left all the passengers needing to enter China, be accommodated, and then rebooked onwards on other carriers - with attendant organisation, delay, visa processing, etc, issues? I guess that simply landing, taking on more fuel, and continuing wasn't an option in this case, so returning to Heathrow would be the best place to go.