Its the same old case of monthly productivity versus Excess Flying Pay.
The blocks time for JFK-HKG-JFK is 31 hours 45 minutes, so 3 rotations per month would result in 12 hours overtime. It may be possible to roster 1 of those rotations across the end/beginning of a month, but only for a few crew. For the remainder of the crew on a hypothetical JFK base, it would be a case of finding all of them 18 hours of work to do while in HKG.
While in HKG (or working around the region) there are hotel and allowances etc, so the case is not so clear cut as comparing the basic cost of a based pilot versus an expat.
The perfect North American base from a productivity/cost point of view is LAX, where 3 rotations adds up to 84 hours exactly.
Crew Scheduling have enough trouble putting together the perfect 84 hour jigsaw for the crews in Toronto, without adding another 50 pilots to the issue.