The turning point is probably not that their behavior changed, but that it began to be exposed. First, when video cameras became easily attainable by regular people (Rodney King), then later, when almost everyone starting carrying a video camera (smart phones).
It happened right around the same time that every citizen was issued a portable audio/video recording device of high quality and the means to share the results.
A phenomenon that coincided with a sudden drought of UFO and Bigfoot sightings, coincidentally.