Ultimately, I think Trump won because a lot of key independent voters cast votes against the Democrats. It's a referendum on the way Democrats have been running campaigns for the past 20 years. See 2016 Democrat Primaries [1] where Hillary Clinton's campaign pulled some shady deals to get Bernie Sanders out of the race. Hopefully, we'll get a legitimate 3rd party one of these days to properly give a referendum on both leading parties. Doubtful, but one still has to dream.
[1] https://en.wikipedia.org/wiki/2016_Democratic_Party_presiden...