I've been giving this some thought and while I am not so sure yet, one thing I can tell is that as a teenager in the 80's and early 90's, I witnessed the end of an era where every genre was exclusive of every others.
There were strict rules, for exemple: you can't mix keyboard and heavy metal - dixit Bruce Dickinson of Iron Maiden around 1985. You can't like Michael Jackson AND Judas Priest. You can't do this or that.
Until bands like Metallica and Slayer came along, we metal heads were at war with punks - as in fighting in the streets and all. Likes mods and rockers before us. You identified with one or the other, and there was no in between.
But then those thrash metal bands showed up and the line began to blur - metal bands were openly citing punk bands among their influences. And everything started becoming way more relaxed. Then the first thing you know, there's footage of James Hetfield with a telecaster and a cowboy hat playing country riffs.
By the end of the 80s, bands were disregarding those boundaries, mixing rap and metal and whatever.
I guess fans also became less rigid in the posturing. Except w/ hip hop.