There are four main factors why Boris Johnson won.
1: He is likeable (in reality a charming psychopath)
2: He plays the fool (Court Jester Syndrome which makes it hard to hold him responsible as long as he does not over do it and loose credibility which he risked doing at one point)
3: He has successfully walked a fine line between avoiding racism yet being acceptable to the increasingly insecure British people who seek authoritarianism.
4: Every one was so bad. Corbyn had no message and Swinson has increasingly unlikeable:
disagreeable, angry, swinging the politically correct banner while being dictatorial indicative of immaturity and naivity.
The question now is what will Boris Johnson view to be in his best interests? To hold onto power as long as possible or to find out and action what is necessary for the good of the British people. In the short term those are two divergent concepts but clearly in the long term they are the perfect marriage, as long as BJ still believes in marriage!