Which one is cause and which one is effect? Hard to say, but I can't dismiss out of hand the notion that the elite culture's bias in 1935-1965 against promoting criminals as big deals didn't take the wind out of the sails of various low-lifes who might have acted upon their desires for notoriety in other eras when the publicity machinery was more favorable.
... the most dogged critic of the film was Bosley Crowther, who wrote three negative reviews, as well as periodically blasting the movie in reviews of other films, and also in a letters column response to unhappy Times readers. The New York Times replaced Crowther as its primary film critic in early 1968, and it was widely speculated that his persistent attacks on Bonnie and Clyde had shown him to be out of touch with current cinema, and weighed heavily in his removal.
Here's the 2009 essay by Stephen Hunter that makes most of my points better than I could.