Why do Southern Democrats perform worse among African-Americans than Northern ones?

[WalterWhite]

From 1976 to 2020, there has been a noticeable trend in voting patterns in African-Americans and Democratic candidates. African-Americans generally prefer Northern Democrats over Southern Democrats.

1976: Carter (D-GA) got 82% of the African-American vote

1980: Carter (D-GA) got 83% of the African-American vote

1984: Mondale (D-MN) got 91% of the African-American vote

1988: Dukakis (D-MA) got 89% of the African-American vote

1992: Clinton (D-AR) got 83% of the African-American vote

1996: Clinton (D-AR) got 84% of the African-American vote

2000: Gore (D-TN) got 90% of the African-American vote

2004: Kerry (D-MA) got 88% of the African-American vote

2008: Obama (D-IL) got 95% of the African-American vote

2012: Obama (D-IL) got 93% of the African-American vote

2016: Clinton (D-NY) got 88% of the African-American vote

2020: Biden (D-DE) got 87% of the African-American vote

The average African-American vote share received by Southern Democrats (Carter, B. Clinton, Gore, and Biden) from 1976 to 2020 is 84.8%. However, the average African-American vote share received by Northern Democrats (Mondale, Dukakis, Kerry, Obama, and H. Clinton) from 1976 to 2020 is 90.7%.

In theory, the opposite should be true. Most African-Americans live in the South, so Southerners should have stronger appeal to these voters than Northerners.

Could it be the politics of Southern Democrats? Do the conservative economics of Southern Democrats alienate enough African-American voters to cause this discrepancy?

Could it be the implicit assumptions many African-Americans have of Southern Democrats? Do some older African-Americans see the Southern Democratic Party as the portion of the Democratic Party still in cahoots with the KKK?

[Devils30]

Because we had a big third party in 1980,1992 and 1996.

[Alben Barkley]

Because we had a big third party in 1980,1992 and 1996.

And for 1976, probably Carter’s ties to Wallace and lingering unease fresh in the minds of black voters about white Southern Democrats played a role.

[TML]

Biden wasn't as inspiring among African Americans (especially younger ones) compared to his immediate predecessors as Democratic presidential nominees, probably in part due to his role in the 1994 Crime Bill.

[Schiff for Senate]

Because we had a big third party in 1980,1992 and 1996.

And for 1976, probably Carter’s ties to Wallace and lingering unease fresh in the minds of black voters about white Southern Democrats played a role.

Alben's and Devils' explanations cover it (I think 1992 should be particularly evident...this is why the Democratic margin would be a much more useful metric).