A few reasons:
- The main motif, ironically appears to be one built out of a white-middle-class industrial complex. Despite very little in terms of a coherent platform, Trump appealed to the emotions of an electorate tired with putting up with the 'elites'. Wall-Street, career politicians, the kinds of people who are far and away from the upper echelons of society (ironic again because they voted for an elite as well, albeit 'self' made). The hatred for Hillary was enough to vote for the honestly of Trump, and he's not many things, but telling things exactly how they are is a strong suit that fits a lot of working class people, however, it comes with a problem.
- The Trump vote also associates his voters (mostly whites) with the things he said, which in many ways are scary if you happen to be a minority of any kind. Xenophobia, homophobia, gender, isalamphobia, etc., were all topics that white people have a vested interest in--ways to keep things the same--retaining systemic power and privilege. There's no saying what may transpire out of a Trump regime, but minorities are worried, some even afraid.
- Along with the vote was a staunch conservative backing, particularly from evangelicals, which, again the irony, voted for a man whose character was absolutely the anti-thesis to the supposed faith of voters. There's apparently a way for the left hand to do what the right doesn't know, and evangelicals were happy to throw their full support in the ring behind Trump despite the hatred of the other (the opposite of a critical Christian tenant).
- Lastly, the number of Democrats who didn't vote was staggering. Almost 6 million didn't arrive at the polls which gave very close votes, particularly in Ohio, Minnesota, maybe Florida, and Vermont. Democrats committed suicide by rigging the nomination in favour of Hillary. It seems many wanted Sanders, and their anger kept them away from the polls and lead to a Trump victory.
There will be a lot of questions over the next four years, in paritcular how many outlier things Trump will actually do rather than things he just said he would. One will leave white people angry, the other will leave minorities afraid.