He didn't try and be cool by doing the "mannequin" challenge, he didn't have celebrity endorsements, he didn't speak the political jargon, and he said a lot things that ordinary American's felt.
He isn't part of a political dynasty, such as the Clinton's/ Obama's or even the Kennedy's.
When it comes to voting people don't care what singers, actors, novelists, news anchors, or anyone who just happens to be famous thinks.
They don't care if the candidate has celebrity friends, they don't care if you want be called "Dave" or "Tony".
They don't care if you like popular music, or can play an instrument, or are a good singer.
People don't want a "cool" President, or even Prime Minister.
They want someone who will get on the job, who doesn't care for opinion polls because they're too busy leading the country.
By no means am I saying that Donald Trump will be the most pragmatic leader, but he isn't cool, he isn't worried about how he looks (if he was he'd do something about his hair!), and he will make decisions without worrying about people's feelings.