It's not white people per se, because whites have been big hip hop supporters even back in the Public Enemy days. Where do you think the love from the Beasties comes from?
There's a mixture of a few things. First and foremost, Jay Z didn't kill hip hop at all. He has his own thing, he can't help that others imitate it. At least he's creative about it and knows when to switch it up. Cash Money and No Limit should be blamed more than him. For one thing, the hip hop fans don't know their history. They're always into the next big thing out and don't care about the classics, unlike fans of other genres. This means that pioneers are extremely hard to come by, and without pioneers, you lack influence.
Since hip hop fans are so damn impressionable, the man has used this to his advantage ever since hip hop became a boom. They blacked out all underground records on BET. They only play widely mainstream stuff on tv and radio when they didn't in the past (it used to be, on the west coast you'd hear west coast style, and on the east coast you'd have east coast style hip hop. It used to be diverse). They do this because they know they can get away with it, and the typical hip hop fan is too impressionable to care.
Since all of these networks play the same songs with similar themes, there becomes a trend. People want to be just like that, and the music's identity is gone. Instead of getting innovators we're left with a bastion of me too's. The record companies and other corportate ceo's see this, cash it in, and the people buy it, making the process repeat.
In summary, the thing that killed hip hop was the fact it became mainstream and a billion dollar revenue business. I remember when I was little kid people were scared of hip hop culture. Now you see it all in commercials, and everyone wants to be hip hop.
