I thought going AMS-HKG-AMS is more expensive than AMS-HKG-(TPE or PVG)-HKG-AMS. CX prices flights beginning/ending in HKG higher than routings which simply go through HKG.

It's a bit like BA ex-EU instead of ex-LHR.

We locals first fly to TPE, then fly from there (backtracking HKG) to our long-haul destinations (LHR, SYD etc.). Thought it works in reverse, though as HK residents we try to skip the last HKG-TPE.