There are a lot of reasons why this election turned out the way it did. Both candidates were widely loathed by half of a polarized country which  made it a difficult sell on both sides. They all knew it would be close and were just trying to keep people from defecting in the last week. 

This is where Giuliani delivered for Trump. He was clearly working with the FBI agents in the New York office and Comey either maliciously or stupidly went with the plan. It was timed perfectly and it worked.