Its not just one factor, its many.
*One parent households. Always cast in a bad light and a large percentage of them have kids who grow up well adjusted and successful, but it does mean that the family can be a little unstable. When you rebel against one parent you usually calm down for the other and behave. If the other parent isnt there then you can just derail.
*Bad area in terms of crimes and poor schools = community of children who disregard education and are influenced by crime on a daily basis.
*TV culture and Black culture in general stereotypes black people to be loud and aggressive. Many people look up to their favourite tv characters/actors and if your's is hoodrat Anisha then you might end up imitating her on a daily basis. (the same can be said for "chav" culture)
*Lack of a work ethic - Why would you work, when Steve round the corner doesnt and he can easily buy the latest games on his benefits, whereas you'll have to work in a low paid job for the next 5 months to save up.
*Drugs - You like the ganja or LSD hits and you want more. You're out of money, so you steal and make money. Illegal entrepreneurial spirit. Sometimes you get caught, or you end up owing a LOT of money and you've got to do some less than tasteful jobs to repay it back.
*Fragmented society -since the 1960's community spirit has been in steady decline. a large percentage of the population dont even know their neighbours. Before if someone saw you causing trouble theyd know who you were and who your parents were and the matter would be dealt with swiftly and effectively. Now people phone the police which can ruin a 15yr olds life and stop them obtaining better jobs in the future.
*If you are harassed everyday by police for the way you dress (ie trackies) and they constantly suspect that you're up to something, no matter what you do or how polite you are, you may never lose the stigma attached. Even if you change your style later on. If you're already in the limelight, you may as well perform a song and dance.
* SWAG/Cool Badass culture. Its cool to be a badboy. The girls like you more, the lads give you respect. Social status within your friend circle and local area is often really important in your teens. It was for me. If the easiest way to be the popular one and get "friends" and likes on fb is to get into trouble then people will do it. By removing only the badass culture from society you'd see an awful lot of crime go down.
*Poverty - Crime rates for low income white males (WLI) are on par with that for low income black males(BLI). Similarly the crime rates for middle class white males (WMC) is on par with the crime rates for middle class black males (BMC). and BMC:BLI = 1:6 and WMC:WLI = 1:3 [not exact figures] It's not a massive coincidence, its a reflection from all that above its disproportionate because there are far more low income black kids than there are middle class black kids. If the tables were turned, the stats would fall dramatically.