Context...

...for previous post.

Three parts of a BBC documentary from 1991.
It doesn't necessarily answer the question "why then and not now?" But it does give one a sense of the complexities of our culture in the late 60s and early 70s.

Artists, in this case, were working to disrupt the indifference of political and cultural institutions on a variety of fronts. Their work often reflected a broadening of the civil rights movement—or at least its energy—to include feminism, gay rights, class, and opposition to the war.

One could argue that then, unlike now, the media was much less homogeneous and certainly less corporate. Narratives that focused on the inhumanity of Vietnam, poverty, and discrimination, were more widely available and consequently had more power in the culture. There was a language for dissent on the left that doesn't really exist today.

Dissent in our current culture and media is largely conservative. A message designed to undo the gains of the broader civil rights movement of the 60s and 70s—a cynical effort to leverage an economically insecure population into believing that it's just too darn expensive to care about war, poverty and civil rights.