Good points gmku.
I was right there in high school when several of these "big name groups" broke in '91. PJ's Ten, Soundgardens's Badmotorfinger, and RHCP's BloodSugarSexMagik were all extremely popular in addition to Nevermind. All had their fans and detractors, but neither was really more popular than the others.
Then a "Cult of Cobain" slowly emerged and reached a fanatical level with his suicide in '94. Suddenly Nirvana was THE group out of all of those above (and several others who had come along by this time, including Tool, STP, NIN, and AIC). This had a lot more to do with Kurt's persona and subsequent mythical status after death than it had to do with Nirvana and their music in my experience. In fact, I distinctly remember many (including me) were moderately to severely disappointed with Nirvana's "In Utero" and the status of Nirvana dipped as a result, especially in light of the fierce competition from several other great albums from big name bands of the time. But after Kurt died that seemed to be forgotten and all of Nirvana's material became extremely popular and even revered.
I never got caught up in all of this and was often criticized as a result by more rabid (and emotive) fans who converted to the "Kurt Cult" seemingly overnight. I simply maintained, as I do to this day, that Nirvana was ONE of the greats and Nevermind ONE of the great '91 releases that helped to usher in grunge/alt in the mainstream, but not THE greatest...just as most every other general rock fan did, at least until Kurt died and they seemingly forgot their previous stance.
Such is the power of cults of personality.