The first and most obvious response is: some do, but not all do.
So how does such a question arise and why would anyone expect there to be an answer?
Your question seems to be more about HRC's campaign strategy, how she has presented this "truth", that women and blacks are her firewall, etc. But remember, it's a CAMPAIGN that we're discussing. It's a CAMPAIGN's version of "truth".
It's more on the order of an assumption - something put out there to be discussed - but it isn't any more than that.
HRC is putting issues about racism, sexism, and so forth to the front.
In fact it's a good thing that these issues are front and center.
I don't agree with HRC's ways and means.
The assertions by HRC, Steinem and Albright, were shudder inducing.
Holy shit, talk about time for a reassessment if that's the extent of "feminist leadership in 2016".
She takes certain "identifiable" constituencies ('black', 'latino', 'female') for granted, as if by right, as being her "base".
Then IMO it isn't good that her campaign goes with a Rovian/Brockian "BernieBro" "BernieSplain" type methodology, which is the lowest of the low kind of politics which doesn't discuss but instead accuses, separates. Creates hate. Her campaign goes what I'll call "dirty" and I don't think this is good for the country, it isn't good for what it does to her supporters, it isn't good for what it makes of those of her supporters who go along with it. It isn't good for what it does to the Democratic party, that's for sure.