"Why do so many Democrats hate Hillary Clinton?"

It's not personal.

Any other establishment neo-liberal who ran, especially this year with

so many citizens fed up with business-as-usual, would be drawing the same kind of fire.

It's intensified in her case by her identification with and participation in her husband's administration's policies -- militarization of foreign policy; NAFTA, the push toward deregulation, particularly of the banks (see, the Great Recession) and telecom companies; the Drug War and mass incarceration; the cruel welfare reforms; embracing austerity and fetishizing balanced budgets.

Additionally, there is her habit of seeing every foreign policy issue as a nail needing hammering by the military, and her close ties to Wall Street and the corporate elite. Finally, she lacks a natural politician's gift for retail politics; she isn't light enough on her feet to pirouette past repeated panders and policy shifts without anyone noticing; belated adoption of progressive positions doesn't play as evolving, it looks like cynicism and politics-as-usual:

Fair or not, many Democratic voters perceive her campaign as a con.

Reading List:
-> The most surreal moment in the Democratic debates came when one of America’s most powerful insiders took umbrage at an accurate characterization of whom she represents. Of Course Hillary Clinton Exemplifies the Establishment by Conor Friedersdorf (The Atlantic).
-> How Neoliberal is Hillary Clinton? by Le Gauchiste (Daily Kos).
-> Neoliberalism from Reagan to Clinton by Gregory Albo (Monthly Review), a review of Surrender: How the Clinton Administration Completed the Reagan Revolution by Michael Meeropol (Ann Arbor: University of Michigan Press, 1998).
-> Hillary Clinton isn’t a champion of women’s rights. She’s the embodiment of corporate feminism. Hillary Clinton’s Empowerment by Kevin Young & Diana C. Sierra Becerra (Jacobin)
-> David Harvey not only looks into the political and economic dangers that surround us now, but also examines the prospects for more socially just alternatives. A Brief History of Neoliberalism by David Harvey (Oxford University Press).
-> If the Democrats lose in November 2016, they can't say they weren't warned: Stop Hillary! by Doug Henwood (2014: Harper's) and Ready for Hillary? Really? by Pierre Guerlain (2013: Truthout).