You're ignoring the fact that black people are more likely than white people to be arrested for minor crime; they're more likely to get prison time for similar crimes; etc.
> or poor.
Ferguson etc showed us that small towns used minor traffic violations as a revenue stream. Someone would have a minor, small, traffic violation and get a fine for it. They would then have to decide between taking time off work to pay he fine (and thus lose their job) or go to pay the fine, if they can pay the fine by the time they have too.
Because many people can't afford to pay the fine they end up in jail.
That's pretty much putting people in jail for being poor, and the US does it a lot.