PoC don't need to explain their voting. But people studying politics should dissect such things.
The voting behavior of different demographics, blacks, whites, latinos, men, women, young voters etc. are all interesting in their own right. It is a valid endeavor to pick any demographic and think about why they vote the way they do. The politically interested mind can learn a lot by attempting to do so, IMO. A lot has been said, for instance, about the resentment that drives working class whites to vote Republican, and therefore against their own economic interests, and it is still a hot topic, not fully understood in all respects as of today.
As for why African Americans in South Carolina preferred Clinton over Sanders, I really have no idea, but I'll give it a shot regardless.
First of all, I think it is not something that should not be overrated.
Consider this: "The Bern" is a pretty recent phenomenon. It is something that has only built up over the last year and in some sense represents an anomaly in post WWII American history, in that suddenly concepts such as "socialism" are on the table. This was unthinkable only a year ago, even in the most liberal pockets of American society.
Made possible by the internet, "The Bern" has propagated through American society and, as is typically, engulfed the most idealistic demographic the fastest, young voters, and from there has spread to other demographics. The time-scale on which it has done so is on the order of a few months. I one takes a look at the nice HuffPo chart with moving poll averages (http://elections.huffingtonpost.com/pollster/2016-national-democratic-primary), one can see this clearly. On average, only a few percent of Americans were "converted" each month, but over the course of a year, the total number has built up.
Now lets turn to African Americans. There are different numbers floating around, but as a rough estimate lets assume that this demographic prefers Clinton over Sanders by a 4 to 1 ratio nationwide. All this really means is that this demographic has been slower to catch "The Bern" in that that they are roughly where the national average was last July. Bernie's approval rating has been steadily rising within this demographic as well, and as far as I understand, the process is underway in a similar fashion as everywhere else: First come the young people, then slowly everyone else.
So, if we want to talk about why African Americans are not voting for Sanders, the question we really have to ask is why "The Bern" has spread at a slightly slower propagation speed within this demographic than within the national average.
This IMO is a pretty difficult question to answer. One has to keep in mind that "months" is an extremely short time-scale in politics. It took white Americans many generations to "come around" to gay marriage. In some sense, it would seem immensely unnatural for any demographic to warm to a "socialist" within months, in a country were "socialism" was considered something akin to an insult amongst politicians up until recently. In reality the big question for Sanders always ever was whether "The Bern" spreading through the US would spread fast enough to reach critical mass before the election.
So I hesitate to ascribe any deeper meaning to the slightly different speeds with which "The Bern" spread through different demographics, but if I had to take a shot at explaining the results of South Carolina, I think the most straight-forward is this: The South is an immensely conservative place, in large parts because of the influence of religion. African Americans are not much different than Caucasian Americans in that respect. However, since the Republican party is now deeply racist, there is no place for conservative African Americans within it. Therefore they turn to the Democratic party, and support the more conservative strains therein. For this reason African Americans are over-represented in the the Southern Democratic party, and at the same time are more conservative than the average Southern Democrat. This seems to be a rather obvious consequence of the arithmetics.
It will be interesting to see what happens when the more liberal states vote. I expect Bernie to do better there, even amongst the demographics within which he is currently behind. I also expect "The Bern" to further spread within the African American demographic. Whether this will matter in the end remains to be seen, but in any case I think the stage has now been set for someone who is "openly socialist" to run for any political office in the US, which is a certainly a positive development.
