I think it may be the preponderance of 3-lane boulevards and wide bike lanes in California (and west of the Mississippi, in general). On such streets, you technically can fit a fourth turning lane on the shoulder (where the bike lane is), which means cars turning right won't be blocked by traffic waiting at the light. And bike traffic tends to be pretty light on those 3-lane boulevards, just because it's very unpleasant to bike with 3 lanes of cars going 45 mph.

By contrast, virtually all the roads in Massachusetts are single-lane, where you gain nothing by letting cars enter the bike lane because there isn't enough room for them to pass the cars in front of them anyway.