I think the lack of a broad, decade-defining genre is a result of the relative maturity of this type of music. It really hasn't been that long since the Beatles...I wonder how many "genres" of classical have either been lost because time smooths over the differentiators. We may, as a society, reach the point where ABBA and NIN are just lumped into the same genre.
Taxonomies evolve from atomically granular to rationally generalized over time. We are somewhere in between...at a stage where almost any new thing can be defined with a compound term: Synthwave, Triphop, Pirate Metal, etc.