The reason is because black youth ran around for over a decade making records and or portraying an image of a thug, murderer and ruthless killer. Rappers set the dress code for this image, black youth emulated it and embraced the persona.
So now after over a decade of black gangsta thug and pants sagging white people are starting to believe it and you blame them?
Watch a video or BET and ask the question
What can be put into question is why this situation exists. And maybe even who is to “blame.” But neither the answer to either of those questions may lead to the solution. And who needs to take responsibility to correct it.