For CX, too many Hong Kong Chinese folks in YVR. Not sure on JL's loads to YVR; last time I rode it the plane was far from full. I think most TYO traffic is still more focused on California than the northwest, and of course many many more OW connections through LAX than anywhere else in the west. I wouldn't be shocked, however, to see CX run an A350 to SEA at some point, or JL a 787. Hainan has switched to a 787 which seems to be the right size, as has ANA from NRT (taking over from United which dropped its NRT nonstop last year.)

For other Asian destinations - PEK, PVG, HKG, NRT, ICN, TPE... there's plenty of nonstop capacity to/from SEA on several carriers.