This is because, as I noted, when cops do bad things the video suddenly isn't available, either because it was turned off, the tape was "lost" or the equipment was "broken" and couldn't record.
Your argument doesn't make sense. Why would people file complaints of actual police misconduct when there's no camera available, but suddenly stop filing those complaints when the camera was there (even if the footage was "lost")?
And that also doesn't address the other statistic, a reduced number of incidents using force. What, are those incidents no longer being reported because officers can throw away the footage? That doesn't make sense either.