Surely the most causal factor is location? The black & minority vote generally goes to Democrats; so presumably in Democrat controlled states any impediments to minority voters would be dealt with promptly.
- Inflexibility in when people may vote; The types of jobs people have access to has a racial bias. Black people tend to have jobs where they literally aren't allowed to leave during they which means they can't stop by the polling location during off hours. This can make polling places deal with larger peaks in predominantly black areas.
- Partisan resource allocation; predominantly black regions tend to lean democrat and so in republican areas they may receive fewer resources to deal with voting.
- Voter ID laws; These also have a racial lean and can clog up regions where they are enacted. Minorities also tend to have a more difficult time gaining access to IDs for voting and so people may have to come back multiple times or be turned away.
- State voting laws; Regions vary with who has access to early voting, vote by mail, etc. These tend to have a racial bias as well.
It's about race.
I mean, you’re basically describing redlining (https://en.m.wikipedia.org/wiki/Redlining) - a textbook case of a “we all already agree that this is racist and it’s not particularly controversial” concept.
You don’t need a law that says “Black people can’t vote” in order to have racist policies!