Well I think one reason that has an effect on the average rapper "making it big" in the game is the way all these rappers "sound" and what they're rappin bout. Think about it, after Pac and Biggies death, you got a million and a half rappers trying to make it in the game w/ the same material on wax and the same sound (like their rhythm n shit too.) No one's gonna know who to buy anymore when they walk down the rap aisly cuz the majority of the names A - Z all are the same "this shit , n that shit" that you can hear on any given cd from any rapper. Thats not putting enough effort into it, you gotta come Real and original.
I mean look at some example's of who's "made it" in the rap game after the deaths. Ludacris. He's got a different style to his voice and his material isn't the same as other cats out there. Eminem, he's got a different style to his voice, and no one can touch his material. Nelly, he brought out that STL sound, along w/ Chingy, and it caught on and got real popular.
You can go on w/ a list of who's got different style and sound who's made it. Missy Elliot, Busta Rhymes, they all sound different and have different styles to their voice when they rap.
I'm not saying that's all it takes to get your shit heard, its just a thought of the top of my head.