1a) Because I used to live in Seattle, YVR is a great international hub and reasonable alternative to SEA for some long-distance flights.
1b) Many miles were earned on CP/AA/CX out of/via YVR before the death of CP.
2) Because I can/did get 500 miles with car rentals, especially ones without flights.
3)It is a hedge against UAL liquidation, and it may become the same for USAirways.
4)YYZ is not a bad hub for some places I travel, and it will be much better when T1 opens
5)Lower status levels
6) It is less hassle to not fly a U.S. carrier across the Atlantic and it is nice to have cleared U.S. Immigration and Customs before arriving at LAX.
7)Tim Horton's coffee and Harvey Burgers at YVR.