While some fly from only YYZ to HKG on those nonstop flights, I would suggest that most are flying xxx to yyy (i.e. any two other airports) via YYZ and/or HKG.
Rod, that's me you are talking about. I first flew CX in 1982 and it was my airline of choice for many years. Most of my travel is trans-Pacific business class, but in the last five years of flying LAX-SGN or YYC-SGN, I have used nearly every non-Chinese airline, except CX.
Why? The fares are ludicrously expensive compared to the competition.