Because it's extremely politically effective.
Divide and conquer.
.
But who started it?
Here was the thing, in 1956, Dwight D. Eisenhower got 36% of the black vote. Nixon got 30% of the black vote in 1960.
Then Barry Deep Down You Know he's Nuts Goldwater decided that (much like Rand Paul) that the Civil Rights Act was a bad idea and he got a whopping 6% of the black vote.
Nixon doubled down on the stupid and persued a Southern Strategy and got 17% of the Black Vote.
Reagan Talked about "Welfare Queens" and "Young Bucks" and got 9% of the black vote in 1984.
Bush Senior said that the mean old black man Willie Horton would stop by to rape your wife if you voted for Dukakis, and he got 10% of the black vote in 1988.
It seems to me the message the GOP has sent is that they aren't interested in the black vote and are happy to villify them if it got them votes.
The only guy who actually tried to break this pattern was George W. Bush, and the right mocked his "Compassionate Conservatism" and "Faith Based Initiatives".
Well, now it's not working for you guys, but much like Cocaine Addiction, you can't stop and eventually it kills you. So you had Mitt Romney (member of a whacky cult that thinks dark skin is a curse from God) making cracks about "Birth Certificates" about the first Black President, and wondering why he only got 6% of the black vote.
But, no, no, it's Democrats "dividing" us on the basis of race and political correctness. I know you really need to believe that, ChiliMac.