Well, to say that she ran a terrible campaign would be an understatement. She had significant party backing, politically and financially, and yet lost to a Republican underdog in Donald Trump. From Fox News’ summary of the report:
Interestingly, the directors of the study dispute the argument that “advertising doesn’t matter” in elections. Clinton’s failure to advertise in certain key states, they argue, was the biggest reason for her defeat by Donald Trump.
The study also backs the view that Clinton’s focus on identity politics and emphasis on condemning her opposition contributed to a campaign message devoid of substance with no clear message on policy.
Published in The Forum: A Journal of Applied Research in Contemporary Politics, the study found that one candidate in particular, Hillary Clinton, “almost ignored discussions of policy.” The study states the lack of advertising effectiveness “may owe to the unusual nature of the presidential campaign with one nonconventional candidate and the other using an unconventional message strategy.”