They mention in the article a bit about the political push against experimental music in the 1930s, but it's interesting to consider that the re-surfacing of such music was also very political: the West were very happy to broadcast free and progressive music across the wall. I definitely have a feeling that experimental music has become a lot more niche since relations softened, the extra funding and promotion has dried up a bit, and now the world of that music has moved almost entirely to the back rooms of various universities.