Most people don't understand that minority voters are on the conservative end of the Democratic party, especially the AA community. Bernie is simply too liberal for these groups. And at least from my experience speaking to some of my AA friends there is some dislike for Bernie because of his Jewish background amongst the AA community idk why though
There are plenty of liberal minorities, the issue is that many conservative ones have been pushed into the Democrat Party by default due to economic circumstances or the state of the national Republican Party. Minorities also tend to place different value on certain issues than white liberals do. It's an awkward alliance that only persists due to the two-party system.
Also I agree with your analysis of the 2008 Dem primary and the 2012 GOP one.