You explained very well on the problem - because the paid fee would make the award ticket has value thus triggers at least 3 US taxes that otherwise would not be there had the ticket is indeed "free", i.e. no value.

For that matter, the award on CX ex HKG now has a lot more taxes due to CX opted to pass along the 3rd runway fee and that is NOT classified as tax, making the award ticket now has $50 or more (forgot the actual amount) taxes and fee than before the 3rd runway fee became in effect.