Every poll except the IBD/TIPP one predicted a Clinton victory. From Why Hillary Clinton Lost: An Election Post-Mortem:
1. Eight years of President Obama operating dictatorially by executive order and edict
[Obama] signed ObamaCare into law without bothering to get even one Republican vote. He almost entirely ignored GOP input on the Dodd-Frank bill that he signed into law — and it’s now blamed by many prominent economists for the worst recovery since the Great Depression.
Even after losing control of Congress in 2012, Obama chose not to work with Republicans, despite his comments to the contrary. Instead, he issued edicts, executive orders that enabled him to act in some cases like a petty dictator without consulting Congress at all.
2. Hillary went from a centrist position against Bernie Sanders in the primaries to the Left in the general election
The typical pattern for a Democratic candidate in a presidential election is to run to the left in the primaries, then move toward the center in the main campaign. Hillary reversed that — and alienated millions of potential voters by doing so.
She talked about tax hikes, about a war on coal and other forms of cheap energy, about a complete government takeover of health care, about further regulating the financial system, and about making the top 1% “pay their fair share.” She promised to hit the American industrial economy hard with new rules to halt the hypothetical evils of climate change.
3. She was the darling of the media the his held in contempt by the average America.
…recent polls [show] that the media is now the most loathed national institution in American civic life. The media are perceived as filled with people who have contempt for average people, along with a profound liberal bias.
4. A history of corruption and scandal
… the Clinton email scandal, the Clinton Family Foundation scandal, and the weird goings-on with former Congressman Anthony Weiner, the estranged husband of Hillary Clinton’s top aide, Huma Abedin, who was found to have thousands of official emails from Hillary’s server on his own unprotected computer.
5. Women voters did not fully support Hillary
What was interesting was how it broke down. Men overwhelmingly supported Trump, 46% to 38% for Hillary. But even women, supposedly Hillary’s most ardent base voters, supported her by just 48% to 44% for Trump. She never really closed the deal.
Read the full article: Why Hillary Clinton Lost: An Election Post-Mortem.