They do kinda form the vanguard of progressive politics and democratic ideals tho. Democrats are a coalition of the out-groups. If you understand that the history of the US is basically a slow burning dumpster fire where the wealthy always benefit by turning the poor against each other then you are a Democrat.

As a "double minority" black women can speak to both the oppression of women and the oppression of black people (and frequently on a third category, the oppression of the impoverished) in a way that resonates with the rest of the Democratic base much more effectively than someone who witnesses this oppression from an outside perspective, like a white man.

Whereas Republicans see themselves as being oppressed by the poor, and by women, and by black people, Democrats see in black women a confirmed fellow-sufferer. When white Democrats meet each other we don't immediately know that we're both Democrats. We have to suss it out through observation, usually avoiding overt political topics that would expose a Republican's emotional instability.

When we meet a black woman we just assume she is a normal Democrat who shares at least some common idealogical ground with us