There was no streaming back then. If you liked the single then you brought the album. Which is i’m quite sure the ALBUM sold more than 1X Platinum.
Never gave a flying fukk about Nirvana or that song so i’m sure somebody else can give a deeper answer regarding the band’s popularity
You don't have to.
Put it this way: you see how disenchanted you are with rap and you wanna hear something that changes EVERYTHING? When Smells Like Teen Spirit dropped, that was the song that a new generation of fans (especially rock of course) got behind, and when MTV started playing it heavy, everyone else followed and they went from small time band to the group that knocked off Michael Jackson from #1. It killed hair bands off. It made everyone dress differently. Groups that came after them from the same city blew up with the same style. It changed how people wrote songs. When that shyt blew up, it made everyone go "ok we're doing this now."
A rap equivalent would be Straight Outta Compton, or Nuthin But A G Thing, something that made everyone drop what they were doing and switch everything up.
The closest thing rap has had to that recently (and it hasn't been nearly as successful but made big time waves in hip-hop) was Don't Like because everyone wanted to jack that drill sound upon hearing it.
You can argue that we'll never see popular music shift off one song the way it did with that.