Why did the art style of photo realism in the 1970s have near instant success?

Because this style was so much closer to both popular audience, which was under the influence of pop art, and art professionals, who were starting to rebel against the unintelligible style of abstract expressionism. Photography had gained its place in the contemporary lifestyle and, from the 19th century onwards, had nearly replaced the classical paintings as a way of documenting reality. This style was a middle-ground of modernity and old-fashioned realism.