Originally Posted by Felix Felicis

Probably the same case as tickets from MNL. CX from MNL to U.S. in Y tends to be competitive and much cheaper than just HKG-USA -- since the alternative would be PR direct to LAX or SFO.
And stopovers in HKG are NOT allowed going to the U.S.; usually free on the way back. Some years ago, I asked CX MNL senior staff why this was so. I was told that some folks actually buy cheap tickets in MNL and hand it off to someone with a similar sounding name in HKG, who then travel onwards to U.S. Hence the "no stopover" outgoing rule.
I wonder if the price for you would drop if you stop in HKG on the return from the U.S. and not going?