millions of dollars of promotion helps a little bit.
real music can fly under the radar, especially in hip hop.
Millions of dollars in promotion? The album was announced outta nowhere, no radio interviews, no tv interviews, no commercials, nothing. They dropped Otis a simple sample flipped by Kanye, no hook, not even a video until after the album dropped, nothing. The biggest commercial they had was probably the listening session and the maybach they chopped up to raise awareness. 2nd single, no video, none of that it just took of through the streets after months they dropped a video with them just standing on stage rapping.
Nas has had amongst the biggest budgets on Def Jam, big commercials, magazines, tv for songs that usually don't get tv play, radio for songs that usually don't get radio play, big videos, actors and all that. (Of course Jay and them have a big budget as well, but they can always do what they want cause their private pockets are very deep). shyt I've his videos in the top on youtube for months now. He has platinum rapper promotion.
So no that not it, it's about Jay-z and Kanye being a lot more interesting to a broader audience. The biggest reason being that they have interesting lives and they are a lot more versatile.