I think (having seen both Washington and California) that there are very different views of the cops in both places. Is it because the police act differently? I don't know.
In CA a lot of people are more likely to believe that the cops are unjust and "out to get them" whether they are guilty or innocent. I can see how CA would have a lot of complaints simply because whatever the cops do, there are a lot of civilians that will automatically think that the cops are wrong. For this reason the complaints might become fewer when there is video proof. It isn't necessarily because cops are monsters when they aren't monitored.
In WA the civilians are more willing to give both the cops and the civilian the benefit of the doubt rather than assume that either one is automatically wrong, so why complain if there is no video proof unless you have a serious problem with the cop's behavior? There is just as much chance that people will believe the cop is telling the truth as they will believe the person. With this in mind there may be closer to the same number of complaints before the videos as there are with the video.