This. Additionally, many of the public records laws in place across the country establish standards and procedures that often involve curation of records before release -- which in turn can involve multiple agencies/bureaus/jurisdictions beyond the PD that "owns" the video. The various policies and procedures that have evolved to meet these often myriad and byzantine policy frameworks are often barely able to scale to textual, digital records. When you expand them to accommodate frame-by-frame review and redaction of video prior to release, the issue becomes far less black-and-white than many of the comments make it out to be (in either direction.)
As a fun exercise, extrapolate this to the data that will be created once mass sensor data becomes 'public record' as the IoT becomes adopted by governments.