Why the sudden hate for classic rock/metal?

I am a huge classic rock/metal fan but recently, in many music circles across Reddit, I have seen a lot of people, especially alternative and rap music fans, dishing out hate towards classic rock bands which are not progressive (for eg: Guns N Roses, AC/DC, Van Halen, Journey, Aerosmith, Kiss and the rest).

Even if you go to sites like RateYourMusic and see the reviews for albums such as "Appetite For Destruction" only recently have they started to become very negative.

Any idea why this is happening? Because a few years back these same bands were very fondly looked upon by many and the rest neither loved them nor explicitly hated them either