Seattle is a no name market, no matter how good they are. San Fran is a huge market that is also good. Money will pile onto San Fran the whole week. Early action can just be US based "locals" building a position on SF for the lopsided action they know they will be taking. They take SF +2.5 -110 early then book action on SF -1 on game day (ie SEA +1 +110) for the free roll middle.