Is that really true? Many of my graduate student friends are involved in activism and virtually all of them attend demonstrations on a regular basis. Most of the professors in my department show up, too, and several have spoken about their political work outside of the university. I'm not saying that there aren't "armchair radicals," but I have met more active leftists in academia than anywhere else. Again, there's a lot of work to be done on universities but, at least in the humanities and social sciences, they are in many ways better for promoting left politics than the average workplace.
And I would say that leftist engagement also has a strong correlation with departments that engage in "pomo newspeak." The student movement here is led primarily by students and professors in history, sociology, English, and comp lit. Meanwhile, departments in disciplines that pride themselves on clarity and immediate practical application have pushed hard to keep Chancellor Katehi and cops on campus.