What killed 80's metal was the constant effort to reach the top of the charts, rather than make good music. Look at Warrant, they wanted to release am album entitled "Uncle Tom's Cabin". Well, the label said, "There is no ballad on it. Go make one." So, they made "Cherry Pie". Wellllll, the single was "Cherry Pie", the album was renamed "Cherry Pie", and that became Warrant's bane. Look at Michael Schenker. He was a GOD with UFO. Then, came up with his solo effort, then he tried to reach the top of the charts. It was a never ending cycle. Many great bands released power ballads just to reach stardom, burying the real hard stuff where people could not find. So, do you want to know why 80's metal died? It is because they threw their credibility away.
Now, do you want to know why power metal get the shitty end of the stick? Well, Summarizing from what Dusty from Katagory V said on the old Utah Metal site. "Are you a cover band that plays crappy versions of 80's music? You will draw a crowd. Are you a band that pretends to be angry on stage? You will draw a crowd. Do you scream on stage and jump around like a madman while banging on your instruments? You will have people going, "Man, that's cool, Dude!" However, do you have a guy that can actually sing? What??? Do you worry about time signatures? Time signatures?!? Are you nuts?!? You can actually play your instruments? Sorry, not interested."
Sorry for the rant.