Personally I think its more to do with location

She moved to Arkansas and met with bill and following that, her involvement with POC and issues which resonate with them, seemed to increase. I happen to believe that when surrounded by racism, white people can either become a part of it, or fight against it. Further, some of the best white allies come from the South, both professional and unsung. Its their deep and daily understanding of racism that tends to do it, rather than the 'theoretical' understanding that so many white people outside these areas seem to hold.

White women, white gay people, white minorities unfortunately, show little natural empathy with people of color despite ther own marginalisation. I see it like poor whites that look on POC and say to themselves; 'Lucky we don't have it as bad'. Making sure they aren't on the 'last rung of the ladder' by if necessary, applying a 'boot to the face' of the black man hanging on there below them.

Bill Clinton was one of those white people, that knew racism and I believe would have taught Hillary much of the realities of living in the south.

In regard to why black people resonate with Hillary rather than Bernie, for myself, I like to call it an instinct: Racism can kill you, if you can't read the signs, to see the clues, to develop a 'feeling' for people who may harbour prejudice with malice. A white person who isn't racist is pretty obvious, a white person with carefully hidden prejudice is the norm unfortunately and a POC has simply to wait for the clues to come tumbling out. I would say Bernie is an old school guy, a sort of professor with his head in the clouds, obsessed about numbers and theorems; when brought to 'earth' and asked about the issues of the day, he is at a loss, clumsy and thoughtless as he has been throughout his campaign when speaking to POC. Those clues, perhaps without malice, nevertheless come tumbling out. They sound like fingers on a chalkboard to me. His online advocates amplify that 'deafening screech' until its unavoidable.

Hillary on the other hand can talk of the issues with a level of understanding that is genuine. Again; instinct. You can't bullshit an understanding of racism to a POC, any-more than an able-bodied man can bullshit what it is like to live 5 years in a wheelchair to a disabled man in a wheelchair. Hillary is old though, as is Bernie. Sometimes we forget how old these people are and how difficult it is for them to resonate on these issues off the back of such a president as Obama who obviously knew the issue inside and out.

It comes to this; for Hillary to cheat the black vote and turn her back on them after getting their votes, would require her to knowingly backstab them. That would be an evil act. Bernie would do it through ignorance, which is far too easy. In addition, his followers, similarly ignorant, wouldn't see any issue with him doing so.