IMO the polls did not show an ethnicity breakdown.They could only rely on the old census population. I don't trust polls.
That said, there are several reasons but I won't get into all of them. I watched the news comparing the 2008 & 2012 numbers turn out for President Obama against Clinton's 2016 polls. Wrong! All black generations and ages voted for the first black man to run for president. Many had no idea how Washington actually worked and didn't care. They just wanted their "son" elected to the highest office in the world. Many African-Americans did not see that wall erected against this "Negro."
One of the oldest Republican politiations made the remark, ok he's in but he will not see a second term, but he did. And that's when that brick wall became stronger.
Back to Clinton’s campaign. Her managers refused to admit that she was the wrong color in comparing turnouts. And that some black folks remembered how President Clinton waged war against black men and the poor. Her managers were in denial.
Yet, President Obama understood, read the tea leaves, and campaigned for Hillary to the point of exhustion. In unspoken words he said, if you love me elect Hillary Clinton. He was fighting for two issues , his legacy and blocking Trump.
Finally the Democrats realizing that Trump had his finger on the pulse of America and jumped in too late to help Hillary Clinton.
I supported Bernie Sanders until the Democratic Party smothered him to save Hillary. Then my only choice was Hillary.
What I learned is nearly half the nation is indeed prejudice.
Trump doesn't care about what he sees happening. What he realizes is that he now has power to go along with his billions. He is a businessman and a smart marketer.
Nevertheless, someone had better step in and block those campaign promises he made before America is "drained."