I think Clinton won because she was an actual Democrat, and had the approvals of the leadership and the voters of the Party.
Statistically, Clinton voters are more likely to be Democratic ideologues with strong commitments to the party rather than liberalism, specifically. When one bases one's identity upon their political preferences it's no surprise they're going to be very defensive against an outsider like Sanders, who is going against the mythological and longtime leader that Clinton was.
Every Clinton voter I've encountered online and in person strongly identified with the Democratic party. People unimpressed by the Democrats aren't very likely to vote for her, because then she has hardly anything to offer -- Republicans hate Clinton because she's a Democrat but because she's Clinton (especially after Benghazi), and I expect more obstructionism to come her way than would happen in a Sanders presidency. Clinton's pragmatic appeal is illusory when she's really only a Party favorite above all else rather than a respected national figure.