Why do you have so much black on black crime?

Because it is individuals trying to get a leg up in life after being placed at the very bottom of life's social ranks.

Life has been made to be a dog eat dog world, that is, hurting someone else to benefit and get the best in life, but there's really no way to get over on someone who's technically seen as superior to you in everything and every way. So, getting over on someone who's seen as your equal becomes a "reasonable" choice in many minds, when only it's just the individual hurting themselves and falling prey to the environment they've been made to live in.