East Coast schools have been around longer, have more prestige associated with their NAME. NYC, DC, BOS are all large legal markets, while San Diego falls well behind the other two on the west coast. Also, on the east of the schools you mentioned, only UVA is public. On the West, all the UCs are public. Publics kind of suffer in the rankings a bit.
You kind of see it in undergrads too, the more prestigious schools (heck all the IVYs) are in the east, and that goes with the law school. Just the way this country developed historically, I guess