Subcultures were the main creative cultural force from roughly 1975 to 2000, when they stopped working. Why?

One reason—among several—is that as soon as subcultures start getting really interesting, they get invaded by muggles, who ruin them. Subcultures have a predictable lifecycle, in which popularity causes death. Eventually—around 2000—everyone understood this, and gave up hoping some subculture could somehow escape this dynamic.