StephenWeinstein
California has more voters, but:
1) Its primary is too late to make a difference (the last time it actually mattered was in 1968).
2) In the general election, if the Democrats usually win California, and if they don't win the California, they weren't going to win the election anyway. In any election where both parties have a chance in the general election, the Democrats will win California, so there's no reason to focus it. (In 1972 and 1984, the Republicans won 49 out of 50 states, including California, but since the Republicans also won 48 other states, the Democrats still would have lost the election even if they won California.)
ms manners
The candidates focus on states that aren't already in the Democrat's pockets.
The Arbiter of common sense
California votes blue. Has for many decades. The candidates focus on the states up for grabs, not the ones they know they will win or lose.
Arch
California is considered a lock for the Democratic party. No point in either candidate wasting money there.
Bernd
California is a blue state in most elections. Thus they can focus on the swing states. Politics much ?