Blacks are less likely to have birth certificates (because of racism). They are less likely to have documents where all the names match (because of racism). They are less likely to own vehicles (because of the poverty engendered by racism) and thus less likely both to have drivers' licenses and to have the means of getting to a DMV. They are more likely to be fired for taking time off work to go to the DMV (because of racism). They are more likely to move in a given period of time (because of the social dislocations created by racism), thus less likely to have the required ID that matches the current address. And they are less likely to be educated about the need for such an ID (because of racism). They are also (because of racism) less likely to be permitted to vote than a white person whose ID is technically ineligible but sympathetic registrars understand the situation and let it slide.