Most of them seem to have very limited knowledge of music in general. Many people agree that Gangsta Rap died in the late 90's, and the "bling, bitchs'n'swag" type of rap has been in decline since 2010. Underground rap is never mentioned.
Similarly, the 90's to them are only about Grunge and Nirvana. Never a mention of the awful late 90's boybands, bubblegum pop and alt rock. In fact, everything non-rock between the early seventies and the late 2000's might as well not exist to them. I've never seen a defener talking about funk, or disco, or house, not even Nu-\M/ETAL which was pretty big as recent as ten years ago. Probably figures since most of them are tweens.