This article touches on the reasons why... here.
Interesting points of note:
"Texas declines to recognize student IDs, it accepts concealed-weapons licenses for voting purposes."
"Thirteen percent of African-American men have lost the suffrage on account of convictions — seven times the national average."
The Challenge of Obtaining Voter Identification
PA State Secretary Announces New Voter ID Card to act as safety net
National Survey Shows Support for Voter ID Laws Strongest Among Those with Negative Attitudes Toward African Americans
Justice Department Investigates Pennsylvania Voter ID Law
State by State Voter ID Laws