It is due to the Gulf Stream. I’ve been flying back and forth for years to Japan and it makes little difference if the destination/point of origin is LAX, SFO, SEA, ORD, MSP . . . they all follow the Aleutians over the Pacific.
I made very minor contributions to this project in my prior life.
https://en.wikipedia.org/wiki/Next_Generation_Air_Transportation_System
btt!!