Blacks (by and large) began their participation in American politics as Republicans. Party of Lincoln and all that. All of my grandparents were lifelong Republicans, as were all of my great-grandparents. My parents' generation split about 50/50 on party lines. In my generation, the capture and herding of blacks onto the Democrat plantation was pretty much complete.
It's a long road back to political independence for most black people. I made my own escape during the Clinton years, but then I've always been the type who seeks my own way. I suppose those with the herd mentality just have to be let down and abused for decades before they clearly see they've been had.
Perhaps now is that time.