I don't know how old you are, but having been a child/teen in that era - that album cover was ICONIC. Nirvana had other albums that were very successful, but those albums' cover art was never as ubiquitous as Nevermind. Heck, a small cut of poster sales alone would probably net this guy a few hundred k.
I'm previous generation from you (OK boomer!) but I bought the cd as soon as I saw the video for "smells like teen spirit". That album, Alice in chains, Soundgarden, Stone Temple Pilots, all just as good as Led Zeppelin, Pink Floyd and The Beatles, the music I grew up with. They all had some iconic album covers, but I'm really not sure the cover has much to do with how many albums sell. Look at the Beatles white album, or Metallica's black album.
