Popular music moves in much slower cycles these days. There was so much innovation in the latter half of the twentieth century, then it all slowed down. Grime for instance has been around since the early 00s, its nearly 2020 now, its predecessor 'UK garage' - spanned the second half of the 90s. How long did punk last before it became known as post-punk? Two years? 'Dance' music's rapid progression in the 80s and 90s stopped almost dead by the end of the millennium. The amazing array of genres, each lasting a few years before the scenes died, was akin to the explosion of rock in the 60s. Its the same in America and hip hop. The 80s for hip hop went from its raw beginnings with 'two turntables and a microphone', until they started using synthesizers and drum machines, splicing up samples and rhythms, creating some of the most cacophonous music ever. By the late 80s it became mellower, funkier, and by the mid 90s many declared it dead, really, there hasn't been much real progression since then, good music yes, but either repetitive or just slightly different. Simon Reynolds wrote a book on this 'Retromania', I've yet to read it, but I'm sure its excellent.