Artists are agents of invention who attempt to change the dominant conventions (although many individuals operating under the rubric of "artist" have much more pedestrian and commercial goals.)

1.9.1 The avant-garde exposes, devalues, and alters existing conventions in search of new cultural arrangements that could provide new aesthetic... See more

As art would no longer respond to itself, and no longer had any constraints, other human activities could be drawn from the world into its hungry maw. Art was no longer moving forward. Individual artists were free to consume the present, swallow other cultural forms, and twist them into new experiences.

1957 brought the most political international postwar art movement of them all: Situationism, which railed against personality-based individualism and asserted that art is determined by real-world conditions and situations. Artists today still work from that premise.