There are many reasons why Hillary Clinton lost. She has all the charisma of a lump of wood, she defending her husband's extra-curricular shagging which made it hard for anyone to attack Trump's love for exercising his middle leg, the allegations about corruption go all the way back to her days in Little Rock and she played fast and loose with security by refusing to use a government approved server for her official e-mails.
However, the main reason, the one that puts all the others into the shade, was utter stupidity. Take this killer paragraph from a Huffington Post story as proof of that point:
In politics, much like anything else, victory has a thousand fathers and defeat is an orphan. A senior official from Clinton’s campaign noted that they did have a large staff presence in Michigan and Wisconsin (200 and 180 people respectively) while also stressing that one of the reasons they didn’t do more was, in part, because of psychological games they were playing with the Trump campaign. They recognized that Michigan, for example, was a vulnerable state and felt that if they could keep Trump away ― by acting overly confident about their chances ― they would win it by a small margin and with a marginal resource allocation.
Got that? They knew they were weak in Michigan so did not campaign there because they were weak. I can sort of understand Ed Balls not campaigning in his own constituency in 2015 because he did not realise how soft his vote had become, but these idiots knew they were weak, and still did not campaign in the states that lost Clinton the election.
So Clinton lost because she did not deserve to win. It really is as simple as that.