Synthetic

Grunge did not kill hair Metal: debunking the myth. 

You've probably heard this myth your whole life how Grunge "killed hair metal" but I'm going to explain why that is a myth and more than anything a marketing creation to promote Grunge bands (specifically Nirvana). 

Let's go back to the final years of the 80's and the early 90's. Hair Metal or "Pop Metal" or "Glam Metal" (whatever you want to call it) had just about run it's course in general...

By hair metal; this is a reference to bands such as Cinderella, Ratt, Poison, Warrant, Motley Crue, Bon Jovi, Loverboy, Honeymoon Suite, L.A. Guns and soooooooo many others. 

At the height of the glam metal phase, most of the heavyweights of Metal who had been already established for some time and widely considered cornerstone bands of the genre eventually adapted to glam metal to sell more records. Judas Priest for instance released the album 'Turbo' 1986. Ozzy Osbourne also released a glam based album in that same year called 'The Ultimate Sin'. Unless you are a big fan of one or the other, these albums are mostly forgotten from their catalogs. 1986 was the height of glam rock, but it was beginning to fade out by 1990.  

Going into the 1990's, most hair metal bands were left standing on their last leg and things did not look good for them; Poison was beginning to break up due to guitarist C.C. Deville's cocaine problems worsening over time, and Bret Michaels was beginning to develop the rock star ego or what is often called 'lead singer god complex'. Ratt was in trouble due to Robin Crosby's heroin addiction and more than anything, the band could never top their mega hit of 'Round and Round'. Warrant was getting sick after lead singer Jamie Lane had ate too much 'Cherry Pie' and the band lost it's minds, and using them as an example; most of these bands and the L.A. glam scene had become a caricature parody of their former selves. 

There was also the underground "Thrash/Speed Metal" scene that began in the 80's, and bands like Megadeth, Metallica, Slayer and Anthrax arguably had something to do with this, cause they were beginning to peak in popularity going into the 90's. 

My point here is, most of these bands were already on life support before Nirvana even came out and grunge was marketed to the forefront. There were various underground scenes that were beginning to take over and could've easily been picked up and marketed by the music industry. Kurt Cobain admitted before that he got most of his ideas from the Pixies and Sonic Youth, who were big in the underground grunge of the 80's (R.E.M. also was a big underground band in the 80's with that "indie" sound that grunge is associated with, more proof that Nirvana did not create grunge). But further note; these glam bands were about to fizzle out regardless due to all their problems. 

Heavy Metal was still a force by the time Grunge came out; the 'Thrash' or 'Speed Metal' bands (Whatever you prefer to call them) of the 80's were beginning to enjoy great success in the mainstream: Metallica's self titled 'black' album sold millions of records and to this day is one of the highest selling albums in lists. In 1992, Megadeth's single 'Symphony of the Destruction' hit #2 on the Billboard 200 chart and the album 'Countdown to Extinction' is their highest selling record of that decade; Anthrax's album 'Sound of White Noise' debuted at #7 on the Billboard Top 200 albums (an album they made without their lead singer from the 80's). And of course, the last surviving L.A. scene glam band going into the 90's was Guns N Roses and they were still selling millions of records during the height of Grunge. In 1993, Guns N Roses released 'The Spaghetti Incident'. The album debuted at #4 on the Billboard Top 200 charts. That is an album that is mostly forgotten about, but it hit #4 and sold millions upon it's initial release. GNR is also an example of how self-destructive the glam bands were going into the 90's with drug problems and feuds with band members, setting up the table for their own destruction. 

In 1994, while Grunge was still the main force to be reckoned with, Motley Crue released a self titled album without singer Vince Neil that managed to peak at #7 on the Billboard Top 200 chart. 

So no, Grunge and Nirvana did not outright kill Hair Metal. It was already dying by the time they came around.