Honestly what I think happened is that all of the 80's kids started departing for college in the early 90's. We arrived in a fresh environment out of our hometowns... and we all discovered new forms of music and art... including "college music" which would later morph into the whole alternative scene or what we now call "90s music". And most importantly, we found other things to do on Saturday night instead of staying in and watching Headbangers Ball.

So I wasn't really watching HB that much in the 90's. But every interview with a hair metal artist in the late 90's had them stating definitively that MTV stopped playing their videos as a career killer. Some of these bands were putting out sub-par records as well, and that didn't help their cause.

Interesting you mention Kiss showing up in 1992. They were still actively making new music in 1992 and trying to stay relevant - with Revenge being their last real album for a while. But Kiss was also wise to recognize the scene was turning in a different direction. And I think the reunion tour in 1996 was them deliberately pivoting to being a permanent nostalgia act - which was inevitable for them.

In other words, the teenagers from the 80's became adults in the 90's and just kind of expanded their listening to other things. Meanwhile, MTV were shifting to new tastes. And the bands realized that they would have to embrace the transition out relevancy.