This simple comparison can have complex causes:

1) CX doesn't fly to destinations that other airlines have expanded into. We know CX's strategy has always been frequency of existing ports over against expanding aggressively into new ports.

2) The rise of LCC or competitors offering cheaper fares at the HKG hub. At the end of the day, majority of people are "price-conscious" rather than "service-conscious" when it comes to flying. They look for the cheapest ticket.

I can list more but this isn't definitive to say CX is losing momentum, but it can be a ringing bell for CX to "wake up" to and pay attention more to their customers, especially their loyal frequent fliers that actually flies CX on a regular basis.